Whether the local churches are autonomous or not doesn't change the fact that the national convention lacks a backbone. They should have the courage to say something like this, regardless of whether the local parishes follow it:
"RESOLVED, that the Southern Baptist Convention affirms that celebrating openly homosexual relationships is contrary to the faith and values of SBC, and strongly urges SBC-affliated parishes to sever all ties with the Boy Scouts of America and no longer sponsor BSA related scouting events until the Boy Scouts of America abolishes their new policy on this matter"
Even if 99% of SBC affiliated parishes decided to ignore the "recommendation", the SBC could have at least they say "we tried", and they'd be able to tell their maker that on judgment day.
They have taken an official position, but some here are under the mistaken impression that it has some bearing on what the local church does. It does not. (And there are no “parishes” in the SBC, by the way.) I don’t think their maker is confused about where the SBC stands as an official body on this position.