It always starts with blocking CSAM, because just about everyone agrees it's awful and the people who produce and share such content deserve to be sent to prison
But then over time it creeps on and on to other controversial things, like surveilling Nazis. And before too long it's expanded to protestors who attended rallies laws were broken in. And then eventually some radical new government is elected and now anybody who's organising any form or protest is surveilled and quietly disappears
Having laws like this is fine when the ruling party only uses it for things most people would deem net positives (like stopping terrorism and arresting child abusers), but passing laws that break encryption or force invasive logging creates opportunities not only for misuse by authorities but also data breaches and social engineering attempts.
Everyone just memory hole and forget about how they complied with a subpoena to turn over the IP and phone number of a French protestor to EUROPOL, leading to their arrest.
Yep, that happened while they were telling their users they do not log IPs and are secure and will protect your privacy, as they still are.