ONE OF THE WAYS YOU CAN TELL THAT LEFTISM IS A RELIGION IS ITS RELIANCE ON SHUNNING APOSTATES:

As Glenn noted in the very early days of Instapundit, “As the old saying has it, the left looks for heretics and the right looks for converts, and both find what they’re looking for. The effect is no doubt subliminal, but people who treat you like crap are, over time, less persuasive than people who don’t. If people on the Left are so unhappy about how many former allies are changing their views, perhaps they should examine how those allies are treated.”