It is a pity, that now I can not express - there is no free time. I will return - I will necessarily express the opinion.
Rather valuable message
I consider, that you are mistaken. Write to me in PM, we will discuss.
It is a valuable phrase
I consider, that you are not right. I can defend the position. Write to me in PM, we will talk.
I think, that you are mistaken. Let's discuss it.