LeBron and the Los Angeles Lakers are slated to face off against the New Orleans Pelicans in Vegas for the semi-finals of the In-Season Tournament on Thursday ... and when speaking with media members, the four-time champ expressed his frustrations with hearing about yet another act of gun violence.

"It just goes back to what I said before about guns in America," LeBron said Wednesday. "I think it's such a longer conversation, but we're the only ones who keep dealing with this same story, this same conversation every single time it happens, and it just continues to happen."

"The ability to get a gun, the ability to do these things over and over and over, and there's been no change is literally ridiculous. It makes no sense that we continue to lose innocent lives, on campuses, on schools, at shopping markets and movie theaters and all type of stuff. It's just ridiculous."

67-year-old college professor Anthony Polito is accused of opening fire on UNLV's campus ... killing three people and wounding a fourth. Investigators are reportedly looking into whether a recent job rejection played a role in the act.

LeBron -- who has been outspoken against gun violence in the past -- believes lawmakers are asleep at the wheel ... claiming firearms have become even more accessible throughout the country.

"The fact that we haven't changed anything -- it's actually been a lot easier to actually be able to own a firearm, it's stupid."