The main reason I see that people want others to build on a baseplate is that it becomes easier to clear if it is spam.  For instance, would you like to dwand every brick on the ground in a house made of 1x1s?  If its on a baseplate, one hit and it's all gone.  Also, building on a baseplate doesn't restrict circular buildings.  If anything, it can make them better.  Think about it.  Would you like a house with no floor?  Besides, builds can look perfectly fine with a baseplate, even if they arn't square.  Just add a couple things on the plate to make it look like a lawn for instance.  Or make it like a parking lot.  There's tons of ways to make it look just fine.