It's far worse than that: after leaving they continue to talk about us, as someone might do for an unfaithful ex, trashing our reputation. We can be toxic AF here, with little to no warning labels about which spaces have what echo chamber policies in place; only people with extraordinarily thick skins can stand this space, especially for long periods of time.

I don't quite agree. The people that leave silently (the overwhelimingly large majority) don't leave as an active decision, but rather fail to come back because there isn't enough interest (or nagging notifications).

And for people to realize their overton window is scewed to the right it is sufficient to be exposed to left wing ideas, no need to find them reasonable. The regular existence of these ideas in discourse is sufficient.