That userbase level is about when you start getting early - usually non-serious - threats and your privacy as a founder starts to erode. Anybody that builds something successful on the Internet will have to disregard the early threats and push forward (or fold up the tent and go home).
When you have 50k or 100k users and you start removing a few dozen abusive users per day, the odds are some of them will be actual lunatics, and some percentage of those will flip their lids and start targeting you with abuse in a surprisingly obsessive way (because they're actually mentally ill). If you can hide behind a faceless corporation with lots of venture capital, that makes it a lot easier as a founder, as the corporate nameplate and lawyers can perform shield duty. If you're a solo founder or equivalent, you take the full exposed hit.
When you have 50k or 100k users and you start removing a few dozen abusive users per day, the odds are some of them will be actual lunatics, and some percentage of those will flip their lids and start targeting you with abuse in a surprisingly obsessive way (because they're actually mentally ill). If you can hide behind a faceless corporation with lots of venture capital, that makes it a lot easier as a founder, as the corporate nameplate and lawyers can perform shield duty. If you're a solo founder or equivalent, you take the full exposed hit.