Follow-up question: what was the reaction from other European nations and the USA when homosexuality was decriminalised in France? Why weren't similar reforms done in the 1840s and 1850s when other Europeans were liberalising?
The French Constituent Assembly decriminalized homosexual acts (at the time these were termed sodomy/sodomie or pederasty/pédérastie) when it adopted a new penal code in September-October 1791. Homosexual acts were simply not mentioned in this code. There does not appear to have been any debate over the issue; if there was, no record of it has survived. Newspapers did not mention the legal reform either and published memoirs are silent on the issue.
Legislators never provided any explanation for this change. The most that we know is that when Le Pelletier de Saint-Fargeau presented the code to the Assembly, he commented that it punished only "true crimes" and not "those phony offenses created by superstition," by which he likely meant the Christian religion. "Phony offenses" probably referred to blasphemy, heresy, sacrilege, and witchcraft; they may (we can't be certain) also have included bestiality, consensual incest, and sodomy, none of which was mentioned in the penal code. The Code of Municipal Police, however, passed only a few months earlier, did punish "public offenses against decency," which included homosexual or heterosexual acts carried out in public (e.g. in parks). The Napoleonic Penal Code of 1810 maintained the decriminalization of sodomy. There were some judges and officials who wanted to re-establish the crime of sodomy, but their proposals never went anywhere under Napoleon or in the decades afterwards.
It is likely that the legislators were influenced by the philosophy of the 18th-century Enlightenment. While most thinkers considered homosexuality a disgusting and vile behavior, they believed that it ought not to be punished as long as it was consensual and carried out in private. Napoleon himself told the Minister of Justice in 1805: "We are not in a country where the law should concern itself with these offenses. Nature has seen to it that they are not frequent. The scandal of legal proceedings would only tend to multiply them." In the 1830s, a legal dictionary explained that homosexual acts, "however shameful and culpable they may be, no longer appear in our penal legislation [...]. The legislator has limited himself to criminalizing indecent acts that take place in public [...]. [Homosexual] acts, committed in private, [...] do not openly trouble the society that does not know about them and harm only the perpetrators, whom they degrade. [...] What good would it do to unmask so many hidden depravities, so many shameful mysteries?"
Most people were strongly opposed to homosexuality and homosexuals and lesbians encountered ridicule and scorn (at best) and physical violence (at worst). But as long as they did not engage in sex in public places, homosexuals did not have to fear legal penalties in France after 1791. In the early 19th century, many European countries copied French legislation in this matter, although England continued to execute homosexuals until 1835 and to imprison them thereafter.
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Another follow up- how did the average Frenchmen view this? Did homosexuality become accepted/tolerated within society?