No, in the overall sense it is not. I like how you quote only part of my text and not the rest of it. So let me restate what I said a bit differently. If the government fully sanctions gay marriage and continues to remove disincentives to single motherhood, than far more children would be likely to be brought up in such circumstances. Thus the government would be doing these children a disservice through their action. On balance, therefore, the government will serve the greater good by sanctioning only the best possible family structure.
Secondly, what a typically liberal position to state that the government can somehow hurting someone by doing nothing to them. What we are talking about here is providing government sanction and encouragement to practices which are already legal and feasible. Gay couples have kids. Single people have kids. It happens. If you are so certain that these children are in good hands (and yes I would even agree that many of them are), why would it be "turning our backs on them" if our government simply does not let the parents get officially "married"?
Furthermore, it is not the government's fault that voluntary single mothers and homosexual couples make the selfish choice to create a child knowing it will not be raised in the best possible family structure. Would you also blame the government for doing a disservice to a child by putting his convicted felon's parent in jail? Of course not. And neither should you blame the government here. So put the blame where it is due here.
This quote is yours, but the emphasis is mine:
Children deserve to have their interests looked after no matter what situation they find themselves in. They don't choose their parents.
EXACTLY. And that is why it is selfish for voluntary single mothers and homosexual parents to choose to have kids---because they bring a new life into a knowingly disadvantaged family structure without their consent. Again, put the blame where it is due.