They're in direct competition with each other. It shouldn't surprise anyone when people take a side. When people on the left describe themselves as "tolerant" it's because they are typically tolerant of more individual things, not because their tolerance is equally spread among all things.
showing willingness to allow the existence of opinions or behaviour that one does not necessarily agree with.
You don't get to pick and choose individual things to be tolerant of, you don't get to pick a side and then not be tolerant of the other side, that's just not tolerance.
(What you can to, is to pick one side and then be tolerant, to show willingness to accept the existence of the other side, while seeking to change minds on the other side)
As far as I can tell, it's a label applied by the right to the left to make the left feel guilty. (And that tactic works, is the sad thing.)
If you Google 'tolerant left', you'll find only right-wing folks upset at the left's intolerance. But did the left ever say they wanted to be tolerant?
But for the purposes of this particular thread, the GGP said the left are tolerant, and the GP accepted that premise.
If you want to wear the label "tolerant" you have to tolerate. If you don't want to wear it, well, you still have to tolerate, because that's what civilised people do, but if you don't, at least you're not a hypocrite.