FWIW I'm not saying this is a good thing, or purposeful, but just that if the goal was to eliminate dissent, a whole bunch of people quitting is probably more or less accomplishing the goal.

Person you're replying to was mentioning customers quitting, not employees (and I have seen a number of people mentioning they've cancelled their Basecamp or Hey subscriptions today).

Why do you assume the "activist" personality types left?

Maybe people that never discuss politics at work want the right to do ot too.

Common sense, I guess.

Product managers are not exactly a time critical position. If the iOS app falls behind the Android app for a few months, will many users even notice?

And it won't take them long to re-fill these roles. There's a ton of unmet demand to work at a place that's purged the activists. You aren't gonna see them much on Twitter but Basecamp just gave themselves a massive recruiting advantage that FAANG cannot/will not match, and they already had a good reputation. Lots of people read DHH's blog post and thought "excellent, that's what's needed". Any impact on the firm will be transient at best.