The US can't even confirm how many detainees have died in custody in immigration detention around the country, yet they have precise numbers on how many people the Iranian regime has killed? Give me a break.

Which Iran did not do. There's a single report from an anti-Iran agency saying that Iran claimed 3,000 killed protesters (not 20k-30k). Iran never said that though, and I would challenge anyone to produce evidence that they did.

I find those numbers hard to believe, as it is obvious that the US was already planning a regime changing intervention for quite some time when those protests happened.

You can't trust people who paint Reza Pahlavi as a paragon of human rights and democracy. And neither you can trust every iranian refugee as a lot of those were corrupt members of the ruling government or worse, Savak members.