it straight up does not matter whether eridan "really was casteist" because he did in fact say all of those things, and as cruel as it may seem it actually makes us better communicators not to ignore the words coming out of people's mouths. though the real reason why eridan sucks is because he is a boy, and everybody who may or may not do similar highblood things to him eg vriska, equius, feferi don't suck as much (or in vriska's case, at all) because they are girls. it's really that simple