I don't think most people would give a second thought to paying $1/mo for Twitter, and at that price, it's actually a good idea by Musk. If you weed out people who think twice about paying $1/mo for instant news on their favorite topics (e.g., Shams/Woj for DF users), you're likely getting rid of people who just post ignorant or toxic stuff, while decent content creator types and regular readers who don't post anything will stick around.
It's possible a negligible price point would actually be reverse elastic for the demographics that matter - raising the price from $0 to $1/mo could plausibly increase the userbase among people who are willing to pay, due to the natural sanitization of the content. There's a fine line between $1/mo and whatever Musk is actually thinking about, though. At $5/mo, I'm envisioning a mass exodus to Threads.