Just a few further thoughts . . .
What we now call "second wave" feminism was a movement that emerged alongside other social justice movements in the 60's and 70's - civil rights/racial equality, gay rights, anti-Vietnam war, labour movements, indigenous peoples' rights, many colonial independence movements, etc. Thinking about it, in each of these movements, there were the visionaries and the missionaries, so to speak. Because their ideas of tackling the very much entrenched status quo seemed SO radical at the time, looking back, we tend to remember the visionary leaders and their ideas the most.
I think in general, people were "buoyed up" by so many previously "unthinkable" ideas coming out into the open and the sense that if that could happen, well almost anything could be possible.
There was perhaps a sense that because people were so long kept ignorant, just opening their eyes to the injustice all around them in itself would be transformational. People would see how the political, economic and social traditions and structures were unjust and harmful and would simply stop co-operating with them. And, without that co-operation, those structures would collapse and the result would be a new world order, predicated on fairness and equality.
But, what they didn't predict is that:
a.) Just making people aware of injustice in itself isn't always enough to change minds, let alone behaviour. Social conditioning can be very strong and not everyone is willing or able to take a "leap of faith" and reject "the devil they know," with ease.
b.) The people who benefit directly or indirectly from oppression of others won't necessarily be persuaded by the fairness argument and will actually want to retain their privilege. They are backed by institutions that are quite powerful and well-resourced, so ready, willing and able to defend these privileges.
c.) The oppression people experience is rarely just of one type or from one source, so even refusing to engage with one set of oppressive structures (e.g. feminist separatist, Black separatist, etc.) doesn't mean an end to other forms of oppression (e.g. economic, disability, etc.)
However, that 2nd wave of feminism DID shed light on some of the worst examples of sexual discrimination, leading to significant legal and policy changes like the Equal Pay Act and Sexual Discrimination Act. And, there were other legal changes that countered other overt forms of discrimination, like the Race Relations Act and decriminalisation of homosexuality.
But, these steps still didn't provide the "tools" for addressing more "indirect" and institutional forms of discrimination, and that's where I think the "third wave" of feminism came in - looking at opportunities for working within as well as outwith the "system" to tackle sexual oppression. This included collaboration with other political and social movements against oppression (e.g. racism, disability, immigration, age, class, etc.)
Not surprisingly, at the same time there was a backlash against the perceived gains of pretty well all social justice movements (starting sort of 80's onwards, perhaps not surprisingly in parallel to the Thatcher/Reagan/Bush era,) including feminism. Then in the past 10 to 15 years, there has been the rise of sexualisation and pornification in culture. And, there has been the corresponding advance in communication technology that has enabled those messages to be all pervasive, to become normalised.
I sense that the resurgence in Radical Feminism/Second Wave Feminism is in response to this. And, because it happened on Third Wave Feminists' "watch," they are dubious about whether any of those Third Wave strands of feminism are genuinely up to the task of smashing patriarchal oppression. Some here have used the terms "diluted" and "watered down" to describe non radical feminist strands (often mistakenly bundled together as "Liberal Feminists,") and argue more or less that Feminism needs to return to the fundamentals of the Second Wave.
But if that didn't really "work" first time around, what is different now that means it will work now?