The issuance of legal carry permits for concealed weapons isn't really relevant to a discussion about illegal mass violence that is largely carried out with long rifles.

Of course overall gun violence is dominated by pistols (but I wouldn't expect the people using pistols to commit illegal violence to be overly worried with carry permits).

Carry regulations specifically have loosened. CHL holders are statistically model citizens. They commit significantly less violent crimes than the general public, and significantly less than even trained police officers.

Regulations on purchasing have increased drastically over the last 60 years. It's harder to buy a gun now than it ever has been in this country.