> vote for a party that legitimately changes the law through the defined channels

So what if no party is willing to do that? Gay marriage in many Western countries has consistently had over 50% support going back a long time[0], despite overwhelming polling, no elected governments on Earth were willing to change it except in the last few years. This is the same for other issues like marijuana decriminalisation. By your measure of legitimate change: Who does an American vote for to stop the 20 year war in Afghanistan? [1]

[0] https://en.wikipedia.org/wiki/Same-sex_marriage#Public_opini...

[1] https://www.washingtonpost.com/politics/2020/01/05/this-rece...