IMHO, some training is needed to handle firearms and it makes sense to make it mandatory.
Who do you want to set the standards for mandatory training? Blomberg?
maybe the mayor of Chicago?
Which others of our Bill of Rights do you want mandatory for? 1st, 4th or 5th.
Where in the constitution does it require mandatory training for any of our rights.
Many use the analogy of driving. We require driver training and test to get a operator's license. If training was the answer, then there would be no traffic accidents.