Everybody has their own opinion, that's what makes everybody unique and nobody should tell somebody their opinion is wrong because to somebody else that opinion may be right.

"It may be your opinion, but your basis is way off" is a better way to express how their thinking may be flawed. But an opinion is hardly wrong--just not yours.

What if their opinion is that they should tell everyone with a different opionion that their opinion is wrong?

Not that I agree with this.