Bipedal Pokemon are not inherently shit. It's not simply that they are bipedal. Charizard/Blastoise are not bad Pokemon.

However, I believe there is a correlation. There is something that makes many bipedal Pokemon shit. So where is the line crossed? What makes them shit?

I don't believe it's being furry that makes them shit either. There are many bipedal Pokemon that are not furry and yet their designs are detestable in a way that seems to be linked to them being bipedal.