The fact that Eich donated in support of prop 8 does not necessarily make him a homophobe. The only thing we see is the donation and none of the context around what made him decide to do it. He has denied being a homophobe and there have been no reports of any homophobic behaviour. The only thing we actually know is that he made a donation to a political cause that the majority of the voting public also agreed with. Is it fair to say that every single one of the 52%[1] of voters in support of prop 8 are homophobes? Plainly the answer is no.
[0]: http://en.wikipedia.org/wiki/Fundamental_attribution_error [1]: http://en.wikipedia.org/wiki/California_Proposition_8_(2008)...