I contest both opinions:

1. More and more people care about this, eg journalists, politicians, etc. Apple has been talking about this a lot, although some being propaganda for messages, but their customers are already somewhat aware of private messenging.

2. It may not degrade ad targeting that much. I imagine doomscrolling does it way more: you engaged with this post, you ignored that one, and so on.

for 2, I will say anecdotally I have never in my life bought something directly from an ad until the last 2 years on instagram. It actually found things directly useful to me that I did not know about beforehand (I did still go through an hour of research or so, but was amazed at the algorithm discovery capability)