You are correct on ethical and political grounds. One has the right to say what he feels (given that it does not violate other people's rights). So, if X is feeling that he can scientifically disprove God, then there is, indeed, nothing "wrong" with doing so regardless of whether it is needed to do so. However, I was not focusing on the ethical and political aspect of the question.
In addition, my feeling of I can do X does not entails that I needs to do X (or I should do X).
For example, I may feel that I can apply lipstick on my lips (indeed I can as a matter of fact, because my hands are not tied in a way that I am unable to reach the lipstick, for example). However, it does not mean that I needs to apply lipstick. (There is no ethical concern with applying lipstick either. It is simply unnecessary for a boy like me.)
