> This is a strawman, mentally ill individuals who have been diagnosed as such are already barred from possessing firearms.

So, shall be infringed in certain scenarios?

The infringement is limited to a very specific class of people who are a small subset of the general population. Consider that convicted felons may not own firearms, is that an infringement? I would argue that it is not, as you lose certain rights when you are convicted, just as you lose certain rights when you are deemed to be mentally ill or of unsound mind.

In other words, we agree "shall not be infringed" has exceptions, and are just haggling over where the line is.

Your wording is misleading. That applies to people who have been court committed (even the majority of hospitalizations are voluntary or tagged 'voluntary' as a courtesy), or deemed 'mentally defective' by a court. That is a much higher bar than what you wrote. There are plenty of people with mental health diagnoses who have never been court committed.