1960's-1970s celebrity culture was full of young groupies sleeping with older men. Bowie, Jagger, Ozzy, etc were all doing it, and often brazen about it, so its not overly surprising that European intellectuals just wanted it formalized as they were doing it too. They felt it harmless enough for their own selfish reasons and wrapped it up into a 'autonomy of self' argument that, of course, was very self-serving. I think this is good evidence that when you stray outside of your specialty (adult ethics) then you can make some obvious mistakes in other specialized fields (children's sexuality). It probably doesn't help that you have both a strong anti-authoritarian movement and sexual revolution movement happening at the same time, which only added fuel to this fire.

Its still wrong, but anachronistically wrong a bit like how many elements the founding fathers put in which are good government but did so under the unforgivable sin of slavery. If that's too 'ancient history' for you, let's consider Brendan Eich's contribution to Firefox but also understand he is a homophobe. We can still use and appreciate Firefox's technical advancements without worrying about Eich's homophobia.

Age of consent skeptics are as old as time anyway. It rages on today in the modern libertarian party and incel culture. Anti-authoritarian and reactionary movements often become victimizers of children and women and racial/religious minorities because these groups are often protected by authority. When you remove authority, suddenly they are powerless and easy prey to whatever replaces that authority. The most obvious example are soldiers raping women in towns they take over.