You're partly correct. It's a warning to people to consider the slippery slope they're standing on. There's a perfectly valid liberal argument that differentiates paedophilia from child abuse - but the sort of people who support almost any cause often don't do the requisite thinking.

This means they'll support anything they're told to support providing someone tells them to on Twitter. That's how echo chambers work. So anyone with the knee-jerk reaction 'I would never defend paedophiles' hasn't considered the issue carefully enough, likewise anyone who supports any niche interest group without considering or questioning the potential of harm it could do in society needs to rethink whether their activism is helpful.