The other answers relate to copyright issues from poaching from other (non stackoverflow) sites. This is good advice, but I thought I would add a comment about the situation about copying from other stackoverflow sites as that was how I interpreted the question.
I do not believe there are any copyright issues when using content from another s.e. site as I would be pretty sure that everything we contribute is owned by stack-exchange (if it is not otherwise infringing someone else's copyright). However I would be pretty sure that blatant copying or cross posting of identical questions would be frowned upon.
You might see a question on (say) sci-fi and fantasy, and think that you might want to get an opinion from the community here - I would not think it unreasonable to expect you to ask that question in a different way and not just to copy the material.
But the purpose of repeating a question here would be to try to get a different answer from a movie perspective. If the answer on sci-fi was perfectly good, I don't see any reason why you should repeat the question here.