"Hippies" is a way in which people dismissively talk about anti-nuclear activists, and it's both chronologically incorrect (the hippie movement was largely earlier than the anti-nuclear movement) and serves to disparage the expertise that many of those in the anti-nuclear movement had (the most important early group was the Union of Concerned Scientists, made up of scientists and engineers centered around MIT).

To be very brief about it, the American anti-nuclear movement was largely fringe until about 1979. Prior to that, it was made up of some environmental activists who were dubious about nuclear power, and many highly-trained experts (again, in groups like UCS) who thought that the US Atomic Energy Commission and its successors were siting nuclear plants dangerously, and that the US nuclear industry was cavalier about the possibility of risks. Many resented the paternalism that was present in US nuclear agencies and official experts, who took a "trust us, we know what we're doing" approach. But it was small and largely not mainstream.

Construction of new nuclear power plants in the US peaked in 1968, then fell dramatically, with a brief re-surge in 1974, and then fell dramatically. There were no new constructions in 1978 or 1979. This had nothing to do with the power of anti-nuclear activists. This had to do with economics: nuclear power plants are extremely capital-intensive. You have to put up a lot of money up front, and if you are an electrical utility, you hope to make that money back by running the plant efficiently for 30-40 years. The construction cost of the Three Mile Island Generating Station in Pennsylvania, for example, was $400 million in then-day dollars, which is equivalent to about $1.8 billion today.

Local and regional utilities were never entirely sold on nuclear power. They treated it as a "boutique" power source that would diversify their investments in more traditional power sources. The tricky part about the economics of nuclear is that not only do you have to pay a lot up front (and hope nothing goes wrong, etc.), you also have to have some guess about what kinds of power will be cheaper in the future. So if you are a utility, you can either take a long, expensive bet on nuclear, or you can say, well, we'll just use some more coal, or oil, or natural gas, whose plants cost only a fraction of a nuclear plant, and require a lot less of a long-term investment. On the whole, power utilities did the latter, despite some incentives from the US government to invest in nuclear.

The one of the reactors at the Three Mile Island plant suffered a partial core meltdown to massive national attention, in late March 1979. It took six days to get the reactor under control, during which time conflicting information about what was going on was released, and a partial evacuation was ordered for anyone living within 20 miles of the plant. In the end, the reactor was brought under control with no significant radiation releases and no injury or loss of life. Whether you see that as "the safety features worked" or "they barely avoided something more catastrophic" depends on your inclination, but in any case, for many Americans it suddenly made the criticisms of the anti-nuclear activists seem especially pressing and real, and made the "nothing to worry about" dismissals from the government and nuclear industry spokemen seem non-credible. It moved anti-nuclear sentiment into the mainstream, by not only giving the anti-nuclear voices a broad platform (it didn't hurt that the film The China Syndrome, which describes a similar sort of nuclear accident, came out 12 days before the accident, and that the actors involved in the film, Jane Fonda and Michael Douglas, worked to tie the film into the actual accident after the fact — it became one of the top-grossing films of the year), but by making the fears of nuclear accidents and a smug nuclear industry seem especially pressing.

The consequence of TMI was that licensing requirements became more strict and public participation in the siting of reactors became more intense. For plant constructions that had begun prior to the accident but were not yet complete, there were legal challenges. In the end, many plants were built after the accident — but they had all been ordered prior to 1978. So the average construction time rose dramatically. To illustrate it in numbers: it took about five years of construction for a reactor that went online between 1969 and 1977. For reactors that went online in the 1990s, it was over 20 years. The average time for construction had been increasing over time anyway, as an aside. See this graph.

More time spent on construction, licensing, lawsuits, etc., adds cost. It also pushes the start date for making money further into the future, so the profitability time (again, the reactors need to run for decades to be profitable) increases. It also adds uncertainty to the entire enterprise. At the Seabrook Station Nuclear Power Station in New Hampshire, for example, the construction permit was granted in 1976, the construction of one reactor finished in 1986 (ten years), and it didn't go online until 1990. By that time they had cancelled the planned second reactor at the same site. So this is a reactor that started 14 years late and was only running at half of the originally planned capacity. That's not what you want to see if you're the CEO of a power utility — that's a lot of uncertain economics.

Even without the later Chernobyl accident, which galvanized public opinion even further against nuclear power (though it was a very different sort of reactor and circumstances than any power plants in the USA), the effects of the TMI accident on the industry had made it something that utilities were uninterested in dealing with. There were no new constructions of nuclear plants begun in the United States between 1977 and 2007. Again, this does not mean that no new reactors opened: many of those projects which had been begun prior to 1977 did. The total number of operating power reactors in the USA grew until 1989, at which point it started to decline as reactors were being taken offline (those which were at the end of their service life, or otherwise unprofitable) at a higher rate than new ones were being added. At its peak the US nuclear power industry had around 110 reactors; today it is at 98 reactors in 30 states. But they're getting older and older, and getting decommissioned as they age out of technical and economic viability. In order to even keep that number constant, the US would need to be ordering a lot more reactors per year than it currently is; to make it grow it would need to be ordering a phenomenally greater number.

(This is one of the issues with "nuclear could be the answer to climate change" as an aside — the number of reactors you'd need ordered per year right now would have to be an order of magnitude more than it is if one wanted them to become a more dominant power source in the 5-10 years it will take to bring them online, because most existing reactors are pretty old and will be decommissioned in the next few decades. Maybe they've got a role to play as part of the overall climate change mitigation "mix," but they're not the panacea that some hope. Making a "dent" with nuclear is not as easy as ordering a few more reactors. To just keep the number of reactors constant in the world for the next few decades, construction would need to be doubled. To talk about increasing it significantly, you've got to do things like have construction be 10X or more its present level. That's non-trivial commitment. Personally I don't foresee that happening.)

To return to the original question: did anti-nuclear activism play a role in the long period of no new reactor orders and construction in the USA? To a degree, yes. But to blame it all on them, much less on "hippies," misses much of the point. The economics of nuclear power was already becoming unfavorable and uncertain by the mid-1970s. Anti-nuclear activism was a small and relatively fringe activity in the United States until there was a significant accident. The growing public suspicion catalyzed the economic problems, and killed the appetite for nuclear power by utilities that were already only viewing it as a small part of their overall business.

We can ask hypotheticals like, "would things have been different if there were no anti-nuclear activists, or anti-nuclear activists had no voice in the question of the siting of nuclear power stations?" It is worth noting that in many other countries, "public voice" is heavily devalued in favor of expert opinion. This is the case in many European nations (in France and Germany, for example), and certainly the case in nations under more authoritarian forms of governance (e.g., China). Even in these countries, nuclear power is expensive, and the rate of growth in the nuclear sector has been characterized by fits and starts. (When looking at that graph, remember that reactors take time to build before they start up: shift it to the left by 5-10 years to think about when the reactors were ordered.) (Even in non-capitalist societies, one still needs to meet quotas within a reasonable expense of resources, so economics still matters, even if it is not as obviously acute as it is in the for-profit energy sector.) One cannot simply blame the American anti-nuclear activists, or anti-nuclear activism, for the problems that the nuclear industry has had in getting a strong foothold. American hippies have no bearing on Chinese reactor developments, to put it pithily.