Asking the question "what if we're at the limit for intelligence already?" provokes the answer "but we could always speed up the thinking process and create a faster brain, which would create better intelligence". But this assumes that faster thinking will definitely result in better intelligence. What if the human brain works less like a computer and more like car traffic, where more speed doesn't necessarily result in more throughput? Maybe there are other factors we need to consider besides speed. What might those be?

This, to me, is a valuable exercise. Barring people from asking questions that don't propose solutions seems like a good way to squash creativity, to me.