Ameliorationist

Near-synonym: reformist

Source: wiktionary

This issue […] recalled for me a similar issue that was hot back in the waning days of Amerika's war on Indo-China, i.e., the rights of homosexuals to serve honorably in the military […] At that time, many homosexual activists ― certainly the more politically radical ― took a position contrary to the one voiced by the more Respectable (and institutionally-affiliated) gays. The radical queers possessed a thorough criticism of society; the ameliorationists didn't. The radicals said it was more important to wreck the Amerikan military machine rather than funneling gays into GI rags.

Source: wiktionary