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Aaron Carter's tackling 2 hot button issues ... mental health, specifically his own, and gun control laws -- and insisting it's not only safe for him to own assault weapons but an absolute necessity.

The singer and his mom were at LAX when we talked to him about his recent revelation that he got his license to own a gun. Aaron says he aced his background check, but the fact is police have made several wellness checks to his homes in recent years -- mostly because loved ones were concerned about his mental health

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That's all behind him, apparently, because Aaron told us his mental stability is off the charts right now. In fact, he got a little defensive, saying on a scale of 1 to 10 ... his mental stability is "infinite" -- despite all he's been through over the years. His mom agreed.

As for why Aaron feels the need to own assault rifles ... his mother gives an interesting reason, and it's supported by a story in the family's history, at least according to Aaron.

As we've reported, Aaron recently went through a nasty breakup with his girlfriend in which she allegedly got violent -- resulting in a restraining order -- and that was just days after cops performed a wellness check.

Of course, Carter also had his background check flagged when he tried to make a gun purchase 2 years ago around the same time he entered rehab.