The original post is from /r/space, here, and claims that NASA's post-Apollo plans included a moon base, permanent space station, and ultimately a Mars mission. These were cut short, it argues, when Nixon cut Apollo over its connection with Kennedy and the Democrats, and starved NASA of further funding, forcing it to attempt an ambitious plan to build a reusable orbiter (the space shuttle), which also failed.
The post conspicuously lacks sources, and plays into the common (but overly simplistic) narrative notion of Nixon as a spiteful, unreasonable actor. So, is there any truth to any of this? Did NASA have post-Apollo plans related to the moon or Mars, and if so why were they abandoned?
Yes, NASA and the federal government did have policy proposals that called for a moon base / lunar orbit station and Mars Mission in the 1980s. http://www.hq.nasa.gov/office/pao/History/taskgrp.html
But this is a long term planning document, much like today, saying we could go to Mars in the 2030s if we decide to spend the money. But if you read it closely, it also calls for development of the space shuttle (STS).
I also read the original post and it is one sided. Every decision in history is complex. I can't eliminate ego as a factor, but there were several other factors that were certainly at least equally important.
Money - Nixon was in process of escalating the Vietnam War and implementing LBJ's Great Society Programs, etc. The federal budget was stretched and something had to give.
Public / Congressional Support - Also related to #1. The public wasn't in a rush to get to Mars. People weren't in a rush to spend their money. Much like today, the voter's aren't demanding more space funding. Nixon was paranoid, but Nixon was also in the job of getting Nixon elected. Going against popular opinion would not serve him that way.