Assuming there is no money driven agenda, even the reputable journals have the issue where much of the content doesn't get peer reviewed. The findings are far from concrete.
But money driven agendas definitely exist too, and without basic vetting a journal finds itself hosting bs lobbyist material with sloppy "science" finding favorable results for anti-GMO, alternative medicines, organic farming, anti-vaccine, etc. The problem also exists that these entities are effectively funding their own journals to buy "legitimacy"- and they certainly would pose a threat to any journal that doesn't have high vetting standards.
As of yet, free access journals aren't reputable or actually desirable because they don't have adequate quality control. Free access to information is a worthy and noble goal, but we can't render the information useless in the process.