"I feel like everyone tries to set these concrete rules about what they are/aren't looking for, and I just don't understand the idea of pre-emptively ruling something out if you happen to meet the right person."
Well said, sir! Let me just drop you a quick -- wait, what's this? Why, it's our old friend "Yes, but only if they were obese." With a helpful explanation:
"Look, this isn't about 'unrealistic beauty standards' or 'anorexic models'. I can deal with 'curvy' or even slightly chubby if you carry it well, but if you actually cross the line into being fat or having a belly, it's just not going to work. I don't think that's a lot to ask."
Wow, you sound awfully defensive for a guy who's being totally reasonable, Non-Judgmental Dude.