In the beginning the radical idea is a basic kind of equality where some kind of person shouldn't be disadvantaged for some characteristic.

There is then a growth phase where many people join and small specific victories turn into general victories.

There is then a shrinking phase where people leave the movement or lose zeal as general victories are had.

The movement keeps much of its ideology capital and with the more moderate people losing interest, the median ideology moves towards special privileges for hyper-specific characteristics defended by a very real "the problem still exists".

The end stage is a movement that tries to conflate its extreme views as being equally as beyond question and equally morally right as the views during the growth phase, and you get conflict when people have a hard time sorting out the complexities of which is right and which is too far... and you get the backlash where the basic right is threatened by the connection with the extreme views... and so it goes.

The 21st century is the century of complexity, the basic problems are often solved and the complex ones need more nuance than the basic ones took... and the struggle is getting this point across that things aren't as simple as they were before.