On the downside though, I think it might lead to some thinking why do I need BTC when I can use the facebook "trusted" coin
Only boomers are using facebook these days, and only they will have this kind of thought.
I believe it would be bad, because it will replace tether as a stable coin. I would prefer trueUSD to replace tether, but if its to change tether for facebook coin, then its better to continue using tether, as it provides some entertainment through the irrational tether FUD.
Are presumptions about tether being replaced as strong as bitcoin dying or as strong as bitfinex is going under? Yep, tether and bitfinex is being attacked, and they are quasi-centralized entities that can be attacked, but should we presume their imminent death or even need to be replaced?