I've always had an issue with Research Gate insisting you upload the PDF version of the paper - this is one of the reasons I deleted my account. Many of us are required by funding agencies and/or institutions to make our papers available publicly, and do so either by paying for gold open access or through various repositories (pubmed central, institutional repositories etc) after an embargo period. It would be better if Research Gate would allow users to link to the 'legal' (gold or green) open access version of the paper, rather than uploading the PDF. I think a lot of investigators have uploaded a copyrighted version without understanding if it's allowed, or without realizing there could be copyright issues, assuming there's no problem if Research Gate allows it.