I strongly disagree. He wrote popular science books but I’d argue that they are not that good at all whenever he veers away from his expertise. His stuff on neuroscience is just out there. There is definitely room for scientists who must inspire and inform the public but no one has replaced the era of Feynman and Sagan. Maybe Bill Nye, he seems the most level-headed popular science guy this side of the pond. The likes of Neil and Michio are just lots of air and not much substance and it’s doing science education a great disservice in my opinion.

Kaku used to work with Bunji Sakita, who was the real deal and did a lot of stuff in what is today called hard condensed matter as well (sliding CDWs / phasons / manifestation of N-G bosons). This is real disrespect to the literature, and strongly disagreeing without having read it is pretty worthless.

His books are not good overall? Not much substance? Well, based on relevant ratings on Amazon, the absolute majority of Michio's readers strongly disagree with you. Your mention of Feynman etc. is ridiculous, considering that you have previously talked about comparison with "the average schmuck". Why are you suddenly changing the topic of the conversation?

The majority of his reviews are “average schmucks”.

Would they know if he’s wrong?

That's exactly my point. The OP's question was not about whether he's right or wrong. It was: "why do we care what he thinks ... anymore than what the average schmuck thinks?". The stellar review performance proves that, for the reasons I outlined above, we, average schmucks, do care what he thinks.

I can't think of any common ground between theoretical physics and intergalactic political theory. It just seems like a weak expert fallacy

You are reformulating the original statement and misinterpreting my argument. Do you really think that someone who has graduated from Harvard summa cum laude and earned a Ph.D. from Berkeley as well as having worked at the Institute for Advanced Study and as a multi-decade experience as a professor has the same level of overall understanding of the world around us (including intergalactic political theory, if you insist) as an average Joe or Jane?