If you don't want to be spoiled on a 45 year old show then don't read a forum about a 45 year old show. If you had to post spoilers for TOS every single post would be one big spoiler tag.
I got spoiled on Enterprise because I looked at the forum a couple years after it was over, before I'd seen it to the end. Guess whose fault that was.. mine.
OP, I think it is sweet you erred on the side of caution. It's a big forum and when you're new it's a little nerve wracking to figure out what is acceptable and what isn't at times.