People don't bother saying it just for fun. (Well, some trolls probably do because they just like getting a rise out of people.)

What it's a pretext for varies, though.

When applied to things like participation in athletics, rejecting "trans women are women" just means "trans women can't participate as women in sports". Calling that hellish would be quite hyperbolic. Or you need to fire your Devil and get a new one who knows how to run a hell properly--at least one without casual sports teams and mixed-gender teams.

When applied to things like not getting access to gender-affirming care and instead being hounded and ridiculed and threatened etc., yes, that's hellish.

There is overlap between expression of the two, but not perfect overlap.

Not making the distinction clearly enough and driving the former-only group to silence (who otherwise could partially counteract rather than support the latter) seems dangerous. Literally dangerous.