In recent years this forgetting has been overcome. Thanks to the efforts of Steakley, Richard Plant and Burchhard Jellonek, as well as the publication by Hans Heger [pseud.] of his memoirs, and the play Bent by Martin Shaw, the suffering of gays under the Third Reich has become well known. Now the Holocaust Museum in Washington DC makes sure to explicate the issues involved.
The total number of gays killed seems to have been about 15,000 [figures from Jellonek], mostly by being worked to death. Gays were not sent as gays to extermination camps. This is massively smaller than the devastation visited on Jewish, Gypsy and Serbian populations. But documenting the Nazi attacks on homosexuals is not part of a "catch-up" game with Jews, or other groups. It is rather an exposing of the possible effects of dehumanizing any group.
Recently some members of the American Religious Right [a diverse group that should no more be demonized than any other], have taken to denying the gay holocaust, and in fact asserting that the Nazi part was essentially homosexual. This is nonsense, and not one serious historian countenances the charge. Nevertheless the book - The Pink Swastika - which makes this charge has been subjected to a line by line refutation, available via here.