I really don't know why the way some people's avi's look bother others. Certain things do bother me, (thigh gaps, frowny mouths, etc) but I don't let it affect my SL in any way. If that's the way they choose to look, so be it.
As someone with an avi with a "big butt" I really don't care what other people think. Because at the end of the day, there are circles on SL where that is considered attractive and no I don't have my sliders set to 100.
Sometimes the community goes overboard on how an avi should look and that goes both ways. Everybody's standard of beauty is not the same.