Update: I received a similarly illogical reply (which can be seen with the same link); here's what I said.

Again, I will say - if marriage is to be a truly child-centric institution, then the people desiring to marry ought to already have children. If you object to that, then your motives clearly lie elsewhere in making that claim - most likely in Judeo-Christian tradition. The sources you seem to mainly rely upon are people who strongly identify with the Judeo-Christian faith, which causes me to suspect their motives and integrity in their treatment of this subject. At least if any of them were nontheists, I could rule out homophobia that stems from religious tradition. Alas, the credibility of those you cite - I refer here to outspoken Christians Lopez and Regnerus- is dubious because of the strong religious motivating factor to trump up reasons to disallow same-sex marriage.
Speaking of credibility! Regnerus has, it would seem, misrepresented his findings, as the following demonstrate. His research, many contend, is of dubious merit. http://www.slate.com/blogs/outward/2014/03/04/mark_regnerus_testifies_in_michigan_same_sex_marriage_case_his_study_is.html

http://familyinequality.wordpress.com/2012/06/29/200-researchers-respond-to-regnerus-paper/

http://chronicle.com/blogs/percolator/controversial-gay-parenting-study-is-severely-flawed-journals-audit-finds/30255

The American Sociological Associaton has much to say on the subject as well: http://www.asanet.org/documents/ASA/pdfs/12-144_307_Amicus_%20%28C_%20Gottlieb%29_ASA_Same-Sex_Marriage.pdf

Additionally, if you consider Robert Oscar Lopez your friend, I question your choices - he refers to gay men as  “rutting, uncontrolled animals” in a column he wrote. The more I delve into the people associated with this site, the stranger things get - lying researchers, homophobes who have nevertheless written gay fiction novels...  (http://equalitymatters.org/blog/201307240001)
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Arguing from tradition is fraught with issues (and would you like to argue that Congress is infallible? What happens if I bring up Roe vs. Wade, then? The fact that this misguided DOMA ruling agreed with your notions does not make it correct). Many cultures also had a strong tradition of incestuous marriage - will you defend that as well? Our own country has a tarnished reputation on the matter of marriage tradition also- unless, of course, you think it's acceptable that interracial marriage was banned until the Loving case of 1967! Lots of places have terrible traditions that violate human rights and ought not to be upheld, and this is one of them.
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The "Cinderella effect" refers specifically to stepparents, not to "non-biological" parents. This is a relevant difference; as pHD-holder "EvoBio" says in the amazon review of the book some of that information came from (link here:http://www.amazon.com/review/R2WBAZQA140JLX/ref=cm_cr_pr_cmt?ie=UTF8&ASIN=0300080298#wasThisHelpful),  "It surprises me that, as psychologists, the authors ignored much more likely, psychologically and socially based explanations, such as the fact that step-parents are entering a family that, by definition, has suffered extreme emotional upset (divorce or death, etc.)" Same-sex couples do not always exist under those same circumstances (though some do). Please do not misrepresent the article you cite in this way- it's dishonest. On the subject of child abuse, since you brought it up, the fact that an unplanned pregnancy cannot occur within the confines of a same-sex relationship is actually a great indicator that the child will be able to avoid being abused, as unplanned pregnancy and later child abuse go hand in hand (see http://ecademy.agnesscott.edu/~mzavodny/documents/AERPP_abortionandchildabuse_000.pdf  and http://www.aafp.org/afp/1999/0315/p1577.html#afp19990315p1577-b25). It makes sense that a couple who MUST go through a lengthy,expensive VOLUNTARY process to have a child will really want that child. In addition, according to the second source cited, "[p]overty is the most frequently and persistently noted risk factor for child abuse". Since, as you yourself have pointed out, this process can be expensive, it would seem necessary that that same-sex couple be fairly well-off - and therefore avoid poverty and its associated dangers. The situations are not comparable and that little evo psych blurb you cited does not support your claims.
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In response  to your constant stream of "but they're missing out"-themed comments, here's this little heartwarmer:  http://www.thedailybeast.com/articles/2014/05/30/the-neuroscience-of-my-gay-dad-mom-brain.html
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I can't speak for the children who grew up and are growing up in same-sex households. Though you may have more experience in this realm, and your experiences - whatever they may have been- were definitely valid, you can speak only for yourself.

[This may have posted several times; apologies if it did.]

Do excuse me, I've got a life to get back to.
(I know you can sympathize on that point.)
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Dear readers, I'm tired of dealing with this crazy site now. I think I'll be done.