I looked at that forum and it is far from free-and-open, it is tightly regulated. Although it invites challenges to mainstream science, it requires the OP to promptly defend his/her theory against every objection. Of the 6 ATM threads I looked at, all 6 were closed after post #2 when the OP could not explain how their theory explains existing observational evidence. When they get a personal theory post on another forum, they move it to this ATM forum making it subject to the ATM rules. Via strict enforcement of that rule, they do not allow wild discussions to go on and on. The main different between ATM and PF is that they just close the threads after post #2, rather than deleting them at post #1.