That's his trademark. You don't get to use it. Even if you imagine his departed soul agrees with your cause — which it very well may not — you don't honor him by appropriating his trademark, his identity. It's especially bad to use him in what is for you a fight. The one cause I remember him fighting for was his own intellectual property rights.
As for your social issues... he was opaque. From 2008:
Prince is reportedly "very angry" after the New Yorker accused him of making anti-gay marriage comments, with the Purple One alleging that the magazine misquoted him in a recent interview. According to the article, "When asked about his perspective on social issues — gay marriage, abortion — Prince tapped his Bible and said, 'God came to earth and saw people sticking it wherever and doing it with whatever, and he just cleared it all out.'" However, a Prince source tells Perez Hilton, "What His Purpleness actually did was gesture to the Bible and said he follows what it teaches, referring mainly to the parts about loving everyone and refraining from judgment." "We're very angry he was misquoted," says the insider.I think the best interpretation is that he did not want to be part of your politics.
ADDED: According to Van Jones, Prince engaged in extensive charitable activities and had a religious scruple against getting any publicity for it. One of his endeavors was #YesWeCode — "a national initiative to help 100,000 young women and men from low-opportunity backgrounds find success in the tech sector."