I'm not saying this as someone who agrees with it, but the Digital Millenium Copyright Act is still going to apply to the site's actions even if the members are in favor of this, and the site is the one that would be held liable for posting copyrighted material. The fact that other Verticalscope sites are doing it probably means that none of the copyright holders have filed takedown notices because they're unaware that it's being posted. Or they're aware and don't care, which is doubtful, since failure to enforce copyright protections can weaken a company's copyright claim.
Unless they've repealed certain sections of the DMCA, the forum could have some legal exposure for encouraging this.
"No matter where you go, there you are."