He might have even had some dangerous written materials they should have searched his whole house. Or maybe dangerous chemicals hidden in his closet. Or maybe dangerous weapons stuffed in the couch cushions. They should have ransacked the whole place.
Why even endanger themselves going in with just cuffs? Flashbang the guy before he can react with a possibly deadly weapon. Drive a battering ram through his front door it only takes a second to open fire.
Put him under surveillance for a few weeks and collect his whole schedule so you can hit him when it's safe.
I've been in a similar situation where some agents from the anti terrorism brigade came to my door. Sometimes you just have to shut up and work with them how they see fit.
Nobody was body-slammed, nobody was disrespected, nobody was being held longer than necessary or with excessive force.
This isn't a situation to turn into hate towards the police. Just get over it and don't be a fucking asshole.
I just read a story where a cop visited someone based on a noise complaint and ended up gunning the young Airman down while he was on a video call with his mother and gf... So from my perspective, cops are the danger.