those were all socialist aligned movements:

the civil rights movement -- the black panthers in particular -- was literally socialists and bombed (also literally) because of it. MLK jr.'s cadre took great pains to ensure that their efforts didn't get labeled as socialist because of it. the environmentalists of the 80's/90's -- green peace in particular -- was also heavily socialist influenced and got labeled as such for not making efforts like MLK jr did.

now-a-days, the campaign misinforms americans that leftists don't reliably vote despite examples like clinton and obama proving otherwise and there being enough green, psl, dsa, cpusa votes to counter republicans easily. this misinformation is done to cover for the fact that the democrats don't want to adopt platforms that left leaning voters want and this is most recently self evident in kamala harris' campaign and its attempt to sway republicans to vote democrat rather than shore up her democratic base.