It normalizes age verification online which will likely lead to a less free internet. We could wait for decades until a really privacy-preserving way of age verification will come but what will happen is we'll have to give up our privacy and anonymity to a few large governments and companies.

It opens to door for regulating any kind of communication channels amongst the people. It will start with big social media but it will likely expand to any kind of forums, chats and even open protocols like AT. It will normalize the government interfering in all kinds of online activities.

These may seem distant and abstract to most people but the people in power want or will want to get power over every kind of communication. We should oppose this now, not when it's normalized and has happened for "platforms bigger than X users".

The people should be able to form any kind of group where they communicate freely. If you want to regulate commercial addictive algorithmic content suggestions... OK, maybe, sure. Do it. Don't regulate where people communicate, how they do it, what they talk about and what they share. People who can use the internet, even children, need a way to share their ideas and concerns. They need to be able to belong to whatever community they please.