Anonymity created many, many risks.
There are documented cases of genetic half-siblings having a sexual relationship because they did not know they were donor conceived.
There are documented cases of suicides from adults finding out they were conceived from anonymous sperm donation and that "their Dad was not their Dad."
90% of donor conceived adults do not know they are donor conceived - and so all have provided incorrect medical history information to their doctors. Does that not seem like a risk?
Now how to apply such a law that wouldn't also apply to people who reproduced in the standard fashion but don't want to disclose whom they did so with?
Case three doesn't have much to do with anonymity. Even a non-anonymous donation doesn't mean your parents would tell you about it while still a child
They're more related than it might immediately appear - purposefully choosing an anonymous donor over an open ID donor is often correlated with shame and secrecy around infertility, whereas choosing an open ID donor signifies acceptance, empathy, and a lack of shame/secrecy.
A much higher % of people conceived with an open ID donor are told of their origins.
Are there already such laws?