Right is right and wrong is wrong. You have to stand up for the right thing even if that means telling other people that they are wrong, or even stupid.
You don't have to be smug about it, but that can be a tricky line to walk. Personally, I think it's better to advocate for certain values as respectfully as you know how and not worry about offending people who disagree. Placing too much emphasis on phrasing and tone is what people refer to derisively as "political correctness". It's best to focus more on saying the right thing, and less on how you say it
I would humbly challenge your opening sentences. Right and wrong are constructs of judgement created in the human mind. So while I agree that people should stand for their beliefs I completely disagree that you have any moral authority to tell people they are wrong or stupid. I believe in a free market of ideas protected by the freedom of speech and mutual respect. I also believe that if you want to change someone's point of view you should do so with facts and reason. If your goal is to change someone's thinking outright rejection of their beliefs on the basis of biased judgement and name calling will not achieve your goal and will most likely close that person's mind.
You don't have to be smug about it, but that can be a tricky line to walk. Personally, I think it's better to advocate for certain values as respectfully as you know how and not worry about offending people who disagree. Placing too much emphasis on phrasing and tone is what people refer to derisively as "political correctness". It's best to focus more on saying the right thing, and less on how you say it