Let's face it, TYWD. That's the whole point of any religion. "If you don't believe what we tell you to believe you're the enemy." True, in the modern world things are no longer quite so severe. But I would bet that there are no true religions which give more than lip service to the idea of tolerance of other's beliefs. And the inter-sect wars which are going on in the Middle East right now (Sunni versus Shiia, for example) are not all that different from the way the Catholic Church dealt with Europe for hundreds of years.
As for the Trinity, none of the views can really make sense to anyone. It's a question of faith: you either believe or you don't. To my mind it doesn't matter which way you believe. Chances are you'll be wrong either way.