> Depending on your definition of freedom.
There aren't many definitions of freedom that include state control of your children.
> I‘d vote that‘s a good thing, as it ensures a minimum level of education for every kids.
Whether that's good or bad depends on what that "minimum level of education" is. I know nothing of German schools, but in the US, public schools can (at least in some places) provide a "minimum level of education" that is much more "minimum" than it is "education". It also can be very unsafe.
It also depends on what the "education" is. Imagine that it's 1940 in Germany, or 1970 in East Germany. You have to send your children to public school so that they can receive their education. But the education in question is going to include a fair amount of indoctrination. When you can't opt your children out of being indoctrinated, it's pretty clear that you're not free.
Note well: I'm not claiming that current German education is indoctrination. What I am claiming is that totalitarian regimes make the same argument, and in their case, it is clear that mandatory public education is part of the totalitarian control. So the argument that this gives "opportunity to everyone" is at least suspect, because it may be the "opportunity" to be controlled and indoctrinated.