I apologise, but, in my opinion, you are not right. I suggest it to discuss. Write to me in PM. or
I consider, that you commit an error. Let's discuss it. Write to me in PM, we will talk. or
Unsuccessful idea or
It agree, a remarkable phrase or
Quite right! It is excellent idea. It is ready to support you. or
And variants are possible still? or
I consider, that you commit an error. I can prove it. or
You it is serious? or
I consider, that you are mistaken. I can prove it. or
In it something is also idea excellent, agree with you. or