1) Coinjoin as I see it adds some plausible deniability but the taint is still there. Anonymity is probably not the right word. If one of the input addresses is considered a red flag, all you've done at the end is generate a little extra work for researchers who now need to follow all the outputs to see who took the money.
The way I see it, this is not true. No amount of extra work will enable researches (or whoever) to prove address X is now the owner of the "red flag coins". Any of the output addresses of the coinjoin tx could be the "real" owner.
Please explain if I'm wrong.
You're right, this removes proof that the funds were yours. You have plausible deniability. They only could be yours, as your address is one of those publicly associated with the red flag coins. As you can tell this is somewhat different to the functionality of a tumbler, where at the end of the day your new address is not associated with the red flag coins on the public record.