A lot of people dislike it for the privacy nightmare that it is and feel the threat of an EEE attack. This will also probably not be the last time that a big corporation will insert itself in the Fediverse.
However, people also say that it will help get ActivityPub and the Fediverse go more mainstream and say that corporations don't have that much influence on the Fediverse since people are in control of their own servers.
What a lot of posts have in common is that they want some kind of action to be taken, whether it'd be mass defederating from Threads, or accept them in some way that does not harm the Fediverse as much.
Threads doesn't need to do an EEE attack. They've already gained many more users than the entire Fediverse. At this point, I wouldn't be surprised if they decided to not join the Fediverse at all.
I would never use Threads, but I would use a Mastodon instance that federated with Threads. I already see many journalists and content creators I like trying it out, who either stopped using Mastadon long ago or never even tried it in the first place. If Threads started doing things that negatively affected my experience, I would then switch to a Mastodon instance that wasn't federated with Threads.