To take the easiest point first, I've actually gone out of my way to avoid purism and intolerance of differing viewpoints among those I consider basically allies, even when the difference is on an issue I consider very important. The drive to "purge" one's own side of those who are so impure as to agree with you only 80% of the time instead of 100% can lead only to infighting and weakness, which is why I've always felt cheered to see such purism at work among Republicans and right-wingers generally, while abhorring it among ourselves.
But where the enemy is concerned, there is a difference. The Republican party and the US right wing in general have for years been dominated by a theocratic element which regards non-Christians and any substantial deviation from the Christian taboo system as intolerable or even evil and demonic. The fact that Trump is obviously not religious in this sense has been taken by some as a sign that the right's theocratic tendency is on the wane, but in fact it merely shows that the theocrats are smart enough to support a candidate they consider personally imperfect for the sake of the larger goal of forcing their taboo system on the rest of society. If Trump will sign laws enabling anti-gay discrimination and appoint judges opposed to Roe v. Wade, that's more important to them than his personal lifestyle.
Moreover, the current minority-rule regime headed by Trump is far from clean of the theocratic stench. Stephen Bannon, a major (perhaps the major) power behind the throne, explicitly supports restoring the dominance of "Judeo-Christian values" over the Western world, and views secularism as an enemy to be defeated. As for Mike Pence, another influential figure, his record speaks for itself -- and remember, once enough Republicans overcome their cowardice in the face of the Trumpanzees to help Democrats impeach Trump, it's Pence who will occupy the Presidency.
This is not a mere difference about policy. These people want to impose a totalitarian religious ideology on the entire nation, enforcing its taboos on everybody. They want to make me a second-class citizen in my own country. And this is not something I can just politely disagree about. This is not something I can engage in civil debate about. This is all-out war. I am personally under attack here, and if you're an atheist, or gay, or a woman who values reproductive freedom, or even a religious person of any stripe other than Christian fundamentalist, then you too are under attack. I am not going to treat the people waging or supporting this onslaught as if they were honorable opponents in a normal political contest. One does not respond to blitzkrieg with parliamentary points of order.
"With reasonable men, I will reason; with humane men I will plead; but to tyrants I will give no quarter, nor waste arguments where they will certainly be lost." -- William Lloyd Garrison