आप should never tell someone that their OPINION is wrong... however, if they are stating that it's fact, या आप disagree with the base to their opinion then that's fine. In the end, everyone is entitles to their opinion, whether आप think that it's wrong या not! :)
Well with opinions, आप can't really have a wrong answer. Just tell them that आप disagree and say why. That's the most important part. आप can't tell someone that their idea is bad without having a reason for why it is bad. That's why people should also read Tw*l*ght before bashing it. That way आप can say all the horrible nasty reasons for the book and actually have proof! But I digress, don't tell people their opinion is wrong, because it is an opinion. There is no right answer.
posted एक साल से अधिक पुराना
I have read it and still hate it... but of course... it's your opinion! :)
Only if you're not bichy about it. Everyone is entitled to his/her own opinion. Let them have their opinion, and आप can have yours, and call a truce.
Oh, that doesn't count if their opinion could lead to them hurting themselves (like suicide, "I think I'm worthless") या others (like Hitler and Mussolini).