The R&B crooner posted a lengthy message on social media Sunday, in which he skewered Kelly and what Tank calls his "facilitators" ... including Kelly's team, record company, promoters, and radio stations. He says what he saw on "Surviving R. Kelly" made him come to a realization he wishes he would've reached sooner ... he believes Kelly's accusers.

Tank goes on to say that his 3 daughters will not allow him to continue supporting Kelly, adding that he "choose(s) the lives of these young black girls!" He says enough is enough, and that he's sick to his stomach from the allegations made against the R&B legend ... whom Tank calls a musical genius which so many other artists have tried emulating.

He also ends on an ominous note, claiming there are other men guilty of the same crimes Kelly is being accused of ... adding that society should not let them slip through the cracks.

Tank's firm stance on the issue comes after Lifetime's special wrapped Saturday. A lot of celebs are speaking out against R. Kelly ... including Jada Pinkett Smith.