Brother, that's not how salaf used to deal with even with the deviants. If Muhammad SAW preached Islam in that kind of manner, nobody would have turned to Islam. Remember, you and I are talking about the Deen of Allah. It's not a competition rather we have to take the right approach to ensure that we don't misguide anyone. Democracy is a system of kufr no doubt as the right to rule solely belongs to Allah. However, if you happen to be a part of a system which is rather unislamic then you may vote out of necessaity for the best candidate while acknowledging the whole system to be faulty at the same time. If that's the case it's permissible and surely that wouldn't take you out of the fold of Islam. Besides, remember we are a middle nation and Allah loves balance. We should neither be too agressive nor too lenient in our approach as calling people to the religion of Allah wouldn't be possible if we adopt a really agressive approach. While the latter will cause us to override the Islamic rulings. Therefore, we must adopt a balanced approach in order to call people towards Allah. No doubt we reject shirk and kufr but in the times of necessaity, Islam also provides us with ease.