Sorry but "Stupid" just isn't the word you should use to express that dislike. And blanket judgments and statements are never a good idea.
When the blanket statement is about what I think about certain subjects, then they are a good idea. I know what I think about things, its not like I only dislike some musicals or plays. I dislike all plays and 99.999999999999% of musicals, so I think a blanket statement about my opinion is fine. As for using "stupid", that's what I think about plays/musicals. I can't think of any more appropriate term, so to use another term would be lying
