Read your own article--I already knew what was wrong with it because Scott Alexander misunderstood it on Slate Star Codex in the same way. Bentham believes that all homosexuality is pedophiliac and that therefore homosexuals will have to marry women in order to have relationships that are long-lasting and where their partner reciprocates their affection Therefore, homosexuality doesn't harm straight marriage. That does conclude that homosexuality is harmless, but not by a chain of reasoning we would approve of.