two sheds can you remember where you saw the thing you're talking about where you say it declined when he became leader ? i'd be interested in a link to that.
Fwiw I don't think JC is an antisemite just a bit of a silly old man, too steeped in his little righteous world to be able to learn anything.
I can only speak for myself about the rest of it but the answer to this bit is because i don't expect anything else at all from the tories (or from that boring racist woman down in the village) but i do want better from people - inside & outside the labour party - who are supposed to be interested in making the world a bit less shit than it is.