In my opinion you are not right. I suggest it to discuss. Write to me in PM, we will talk. or
This situation is familiar to me. It is possible to discuss. or
It absolutely not agree with the previous message or
I apologise, but, in my opinion, you are mistaken. Let's discuss it. Write to me in PM, we will communicate. or
I am sorry, that I interrupt you. or
Absolutely with you it agree. In it something is also idea excellent, agree with you. or
On your place I would not do it. or
It is not logical or
Absurdity what that or
You are mistaken. I can defend the position. Write to me in PM. or