Sometimes you would do the same thing anyway if it weren’t an obligation. If that is the case, it’s much more useful to focus on the fact that you want to do that, because obligations carry a negative connotation.
In fact, I think focusing on the ‘should’ may sometimes create the ‘… but I don’t want to’ AndekN mentions above, or at least reinforces it.
Sometimes you would do the same thing anyway if it weren’t an obligation. If that is the case, it’s much more useful to focus on the fact that you want to do that, because obligations carry a negative connotation. In fact, I think focusing on the ‘should’ may sometimes create the ‘… but I don’t want to’ AndekN mentions above, or at least reinforces it.