First of all it's a ludicrous analogy--no one claims alcoholism is an "alternative lifestyle".
Secondly, it could only be remotely considered to be an appropriate analogy if you can prove that all homosexuals are as wantonly irresponsible in their sexual proclivities as avid alcoholics are in their drinking.
Neither habitual alcoholics nor sexually irresponsible people of either orientation should adopt.
People who engage in moderate drinking and people of either orientation who are responsible in their sexual activities should be allowed to adopt.
Kids are very perceptive and will notice right away that the parents are role playing unusual gender roles. If a father dressed up in female clothes and pear necklaces and pranced with a lisp, do you think that would harm the child? If so, specifically why?
So now you're only opposed to effeminate gays adopting? What about all the non-effeminate ones?
The kid would probably be teased by other children, but would probably grow up to be "normal" enough. Mere weirdness does not eliminate people as prospective parents.