The usual thesis is that my freedom ends where your begin and that should apply to the online world too.

Whatever you do that can harm others cannot be tolerated. We should find a way to stop others from being harmed or people will just continue making others suffer without any consequence whatsoever.

So when you see someone sharing child pornography online, that person shouldn't be monitored without their consent? When you have online forums of people discussing the best way to kill another human being probably based on their experience, you shouldn't monitor it without their consent?

You mean there's no online activity that needs surveillance without people's consent?