Backstreet Boys' AJ McLean is all for celebs diving into politics -- a hot topic seeing as how Taylor Swift’s recent endorsement of Kamala Harris has made quite a powerful impact.

We caught up with the singer at LAX ... and he tells us he believes everyone, including big-name stars, has a right to their own opinion, especially if they use their platform for good, and have a positive message.

He admits he's not one to make grand political statements, but he's not shy about who he's backing -- check out the video to see who’s got his vote!

Celebs on the political campaign trail are nothing new ... but Taylor's influence is next-level, telling her 283 million IG followers she supports Kamala on the heels of Tuesday night's fiery debate with Donald Trump.

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In fact, as we reported, a nonprofit org saw a huge spike in people -- especially young folks -- signing up to vote via their online registration tool, surging in the wake of Taylor’s IG post.