Caggiano claims replacing him and singer John Bush will ruin the band's credibility, even though he only joined the group in 2002, well into its distinguished career.
He says on fan website ReunionBashers.com, "They f**ked up! The band should have made new records with John Bush and myself instead of doing this reunion thing.
"I feel like Anthrax lost a lot of momentum by doing this and they also made it a lot harder for anyone to take them seriously as far as 'new' music is concerned. They became a 'nostalgia' act."
But Caggiano's former bandmates insist his claims are "not based in reality" and have asked the rocker to move on with his life.
Guitarist Scott Ian counters, "Without the reunion there was no next record. It's nice to imagine that things would've just gone on from WE'VE COME FOR YOU ALL, but it was impossible. That's it."
"Please stop arguing and complaining about this. Just be happy that we are still here making music and we're all still around to enjoy ourselves."