It's not possible to win every battle, and perhaps more importantly not every perceived win is a real victory. When the battle lines are drawn between friends, and the battlefield is opinion or belief, a misplaced sense of victory will often be much worse than admitting that you can't gain the ground needed for the upper hand. This is not the same as being wrong - right and wrong are most often the basis for your argument but almost never the deciding factor. Your skill in debate is also not the decisive weapon - this might force your opponent's acquiescence but it wont bring you victory. The weapon you need to employ is understanding, and perhaps a little compassion.
It is therefore most important to choose your battles — though perhaps this is a difficult discipline. False victory will harm your friendship. Truly winning is a vanishingly rare prize. An agreement to disagree may well be the best outcome you can hope for. You have to decide if those stakes are worth it — after all friendship is the fruit of discussion. Your righteousness however is no good justification.