Everyone is always hating on Yoko Ono. She's almost universally despised in North America, which I think is pretty culturally revealing. People claim to hate her because she is "weird" and "broke up the Beatles", but beyond that they know almost nothing about her! Yoko Ono was a well-known and respected performance artist before she hooked up with the man whose fame completely overshadowed hers, and she was hugely important in the popularization of performance art and the legitimization of non-traditional art forms. She ran her own avant-garde gallery out of her apartment in New York, and was an early member of the legendary group Fluxus.
I think that the hatred for her stems from some sort of gross cultural inability to shake off the idea of a the siren who drains a mans virility (hence her reputation as the Beatles breaker-upper), and discomfort with the image of a powerful and sexy Asian woman at the height of the Vietnam war.
So I say DON'T DISS YOKO. She's awesome. It's totally fair to hate her if you know her work and have an informed opinion, but no naive hating!