The real issue is a lack of emotional intelligence with a combination of the poorly dubbed psychological issue known as "toxic masculinity".
I've almost finished the eye-opening book "Emotional Intelligence" by Daniel Goleman. I highly recommend reading this book. The author breaks down exactly how the human brain functions on how that affects our thinking.
There has been a recorded steady decline of emotional intelligence in recent generations. Throw into this the change in traditional gender roles since the women's movement began about 50 years ago, and we are left with generations of men who are suffering mentally and emotionally. Men are no longer the sole provider/protector/progenitor as women realized they are not second class citizens. Many men still use the same 4 yardsticks to measure themselves - violence, aggression, social status, and sexual prowess.
So, yes, easy access to firearms will generate more mass murder. However, we also see in nations where private citizens are denied the universal right to defend themselves with arms teenage boys stabbing people to death with screwdrivers. Crime as a whole is decreasing, but violent crimes are increasing.