@Shaul , if you tell a person "I don't necessarily believe you, I don't necessarily like you, I don't necessarily think we can do that, etc" they are going to assume that you don't believe them, don't like them, can't do such and such, etc. Unless followed by a witty statement that says the contrary, I can't think of any situation in which a person isn't going to take it that way.
So, to say something like "I don't necessarily believe you" and expect a person or those around them to not pick up that you're insinuating dishonesty is simply twisting words to twist words, and it makes it hard to have an honest debate that way. Instead, it becomes an argument. What's the point of that? What gets accomplished with an argument? A debate, at least, is meant to bring up points that others may not have thought of, consider new points.
If I wanted to argue, there's a 200 dollar dress I've got my eye on... I'd order that, wait for my husband to object, and at least I'd have something to show for all the bickering...