I agree when you said they have a slimming effect when wearing snug jeans. I also like them when girls wear leggings and a short sweater-dress!
Also, here are some men in Uggs:
I think one reason people don't like men in Uggs is just because it's such a huge trend for women, when it's actually a unisex footwear. I think Uggs even have an overtly masculine shape and design!