I've been reading this thread for days, trying to think about how to answer this question without getting into topics best left for the P&R forum.
- In the US, we have the right to say almost anything
- That doesn't mean there may not be consequences to the speaker or others
- I know there are certain exceptions to that right
- I'd rather not live in a country that didn't have that right
- I don't have to like what people say, and very often don't
- I don't have to let others' opinions change my mind, and very often don't
With that in mind, I'd have to say that "yes, it should be okay to condemn a book without having read it". I cringe even typing the words, but I do believe people have a right to think and say what they want.
I don't have to like it or act on it, although I'm sure I've agreed more than once (e.g., I pretty much agree with the horrible reviews for the 50 Shades books, although I don't think I've read more than a clip or two).
If I really care about the topic being condemned, I have an equal right to offer an opposing opinion. Whether I'd be willing to put up with the dog-pile that would probably arise in such a case, I don't know. I don't have a Twitter account, but I have been involved in some pretty ugly conversations on blog posts in my day.
Sometimes it's easier to shake my head, back away from the computer, and give everyone a few days to calm down.