For example, "building an AI seems hard. no human (even given much longer lifespans) or team of humans will ever be smart enough to build something that leads to an intelligence explosion", or "computing devices that can realistically model an entire human brain (even taking shortcuts on parts that turn out to be irrelevant to intelligence) will be prohibitively expensive and slow" are both plausible.

A short answer to these might note the advancement of applied AI techniques in fields where it was previously common knowledge that "only humans can do that" — e.g. high-quality speech recognition or self-driving cars. I would propose limiting such an answer to "serious" endeavors — ones where humans highly value the outcome, such as understanding a translated message correctly or driving safely — as opposed to games such as chess or TV game-shows.