I wish folks were not so casual about rights.
Not every negative human experience or behavior needs government correction or prevention.
Government has already proven beyond the shadow of any doubt at all that it cannot be trusted to protect rights--its sole legitimate purpose.*
When we start calling for, allowing, or even tacitly assenting to mandatory training, we open the door to all sorts of government-manufactured problems. Too stiff requirements. Too expensive requirements. Too onerus requirements. Essentially we open another door to regulating the right to self-defense out of existence. There are plenty in government who would have no problem setting the bar so very high that few could or would invest the time and money into fulfilling the requirements. And, of course, all this has to have criminal sanctions to give it teeth.
Also, if there are mandatory training requirements, then there is justification to deny gun possession, carry, or use until the training requirements are fulfilled. Translation: Nobody who does not fulfill the requirements can possess, carry, or use the state-of-the-art in self-defense equipment.
*Declaration of Independence
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness. That to secure these rights, governments are instituted among men, deriving their just powers from the consent of the governed.