It's a word like any other. Its neither rude nor polite. It's just a word. Any hint of rudeness comes from the way words are used.
Someone told me once that using the word "should" is rude. Do you agree? If so, what is a good way to replace the word?
Like any other word, it depends on how it's used. Most people use "should" every day without rude intent.
There are times when the word "should' should be used such as "you should not drink and drive". In less important matters you could say "It might be a good idea to..." do this or that.
I was wondering should I answer this question.
I should answer this question.