Such an approach really isn't about "saying yes for the sake of saying yes." We say "Yes, and..." to accept someone's idea as valid and then add to it. This makes other people feel good that their ideas are being acknowledged, it moves the scene forward in a positive way, and doesn't take away from the DM's ability to challenge them.
Why is it the DM's job to validate terrible ideas from an immature player? It's not. Saying "yes, and..." devalues actual good ideas. If someone's too dumb to be clever on a consistent basis, the answer isn't to treat them with kid gloves so they don't get frustrated, it's to treat them like an adult and say, "No". Period. Your idea won't work, so the answer is no.
Acknowledging and validating bad ideas like the "we're here to fix the plumbing" (when there was no plumbing), only further encourages completely off the wall, moronic suggestions. Reading more about how this guy reacts to having his terrible ideas shot down makes me think that guy spent too much of his youth being told he was smart by his entourage when he really isn't, and should have been told to study more. Critical reasoning is not democratic, some people just don't have it, probably because they never bothered to (or maybe they're just too dumb to begin with), and now it's coming back to haunt them.
"Yes, and..." is something I would only do if I were DMing children playing D&D for the first time, but I would wean them off it. It's damaging to children to worry more about their self-esteem than them actually thinking properly. You're not doing them any favors by doing that, they will have no incentive to improve their thought process or to think things through if you treat good and bad ideas as having equal merit.
Countries that worry about grades more than self-worth are generally way more academically successful. This "yes, and..." mentality to me seems like a byproduct of the ongoing infantilization of students in western education. Doing "yes, and...." would only further enable this terrible player to think he's the man. Which he isn't. Sometimes the truth hurts. I wonder if the guy is built or if anyone has ever told him he's dumb to his face. That would do a world of good to a person like this. He's probably not even aware of how bad his ideas are, which is why he's blaming the DM instead of himself (or his parents, or his environment, or his education), which is where the true blame lies.
Majoru's DMing seems fine to me. And yes, I am allowed to judge things. I reserve that right to myself. I agree with some of the other comments that long-term enabling of such behavior is like poor parenting, the fault does like somewhat with the parent as well. But this player is an adult, so it's not the DM's job to teach them how to behave. It is, however, the DM's job to keep his game running smoothly and for that reason alone, this disruptive player should have been booted long ago. Or had this kind of whiney, immature behavior nipped hard.