You are mistaken. Let's discuss it.
I apologise, but, in my opinion, you are not right. I can prove it. Write to me in PM, we will discuss.
I consider, that you commit an error. I suggest it to discuss. Write to me in PM, we will talk.
In my opinion you are mistaken. I can prove it.
Quite right! It seems to me it is good idea. I agree with you.