Billy Bob Thornton Says If A-Rod Gets In Hall Of Fame, All PED Users Have To

Billy Bob Thornton thinks PED users in the Hall Of Fame are kinda like Lay's ... you can't have just one ... saying if A-Rod sneaks into Cooperstown then you gotta let everyone else in too.

BBT came on the "TMZ Sports" TV show and talked about Kenny Lofton's strong comments to us that under no circumstances should A-Rod even be CONSIDERED for the Hall of Fame.

While Thornton wasn't quite as hard on A-Rod as Lofton was (who could be?) he made it clear it's not just about Alex ... 'cause if you vote him in, you gotta vote in a whole generation of cheaters.

Peep the clip -- and be sure to watch "TMZ Sports" weeknights on FS1.