Speaking as a Muslim, I would say that one should first learn about his own faith beyond basic knowledge and proofs, if you don’t, then speaking from experience, you may leave your religion, only to regret doing so later. However, if someone’s level knowledge of their own religion is quite high, then to refuse learning about other religions, in my opinion, may perhaps be a sign of insecurity in your own faith. Of course when learning about another religion, try to learn objectively, it is understandable to have a bias towards your own religion and I’m not saying you shouldn’t, but if you try to learn about something with a complete bias against it, you may miss any beneficial knowledge that may actually be there, and instead reject something simply because there was a latent refusable to understand it; and of course, if you disagree with something, by gaining a better understanding of it, you may be able to better refute it.