I'll also note a lot of objections to the way C++ does backwards compatibility is their adherence to an ABI which they refuse to break, but also refuse to say they'll never break.
Many of the problem that can't be fixed for backward compatibility reasons are because they'd break the ABI, not new code. I think that's very different from other language's policy, which, from the ones I'm more familiar with, is about building old and new code together, rather than linking old and new code together.
It makes for a much more restrictive, but also ambiguous and not guaranteed, set of requirements on any change.
Many of the problem that can't be fixed for backward compatibility reasons are because they'd break the ABI, not new code. I think that's very different from other language's policy, which, from the ones I'm more familiar with, is about building old and new code together, rather than linking old and new code together.
It makes for a much more restrictive, but also ambiguous and not guaranteed, set of requirements on any change.