"After all the thousands of AIDS deaths and all the years of "Safe Sex Is Hot Sex" prevention messages, it has come down to this: many gay men who know the rules of engagement in the age of AIDS are not using condoms. As news of a potentially virulent strain of H.I.V. settles in, gay activists and AIDS prevention workers say they are dismayed and angry that the 25-year-old battle against the disease might have to begin all over again. While many are calling for a renewed commitment to prevention efforts and free condoms, some veterans of the war on...