might his taking on big questions for large numbers of readers do more good than harm?

I doubt it. When you're writing for a popular audience, you're writing for an audience that wants to make up their mind about a particular subject based on your book. They're not likely to weigh it against other points of view, if for no other reason than that they're not likely to invest time in exploring those other points of view. After all, if they were interested enough in the subject to really explore it, they'd be reading about it already, and reaching out to them wouldn't do much to popularize the topic.

Naturally, there will always be a few people who progress from a popular text to a more extensive exploration of the topic, but for everyone else, the topic will tend toward fixation. Which only makes it more difficult for the next writer who happens to be presenting a better substantiated argument.

If you want to get right down to it, popularization isn't a monolith. Some writers are attempting to popularize the current state of knowledge about a subject in order to bring it to a wider swath of the population. Others are attempting to popularize their pet theory in order to sway a general audience who doesn't know the subject well enough to treat it as provisional or even dubious. After all, in any society where scientific research depends at least in part on public funding, popularization is a pathway to money.