I'm a bit late to the blacklist/strike debate, but I wanted to put my 2 cents in, if nobody minds. ^.^
My opinion is sometimes, they are necessary. And, yes, even on public threads. In fact, they tend to be more useful in large threads, but, that said, it's not for every public thread. If there isn't a lot of rulebreaking, no, it's not needed. But in the case of the Swap Threads, a strike/blacklist had to be put in effect due to the sheer amount of people breaking the rules on the thread. You know how many people I warn a day on that thread? At least 5. And 99% of the people I warn, will never break the rules again. Yes, I've had to temp ban one person, and completely ban another this month, but, when you break the rules every time you post, something has to be done. It's not severe enough, in my opinion, to warrant bothering a mod for. Mods, I feel like, have enough on their plate. They can't go around dealing with minor things like people asking for wishlist pets on the Swap Thread. I can do that, and it works. Do I think I'm better than them, just because I can warn them? No. In fact, I hate warning people. I feel bad. I'm actually a lot more lenient then I probably should be, but, I don't want to upset anyone, I just want them to be aware of the rules. Plus, all the strikes are wiped after the end of the month. Everyone who got a warning gets a clean slate at the start of the next month.
Another thread I work for, Cheetah Eggs, has banned people. But never for anything like "I don't like them, I'll ban them." It's normally cases of art theft, or, in one case, they spammed up the thread constantly. Mostly it's for serious rule infractions, not just little things.
TL;DR, black/strike lists can be helpful, but only in certain situations.