The retirement population will become the single greatest voting block in America with the coming population pyramid inversion. You would be delusional to propose that this voting block will allow Social Security and Medicare funding to go bankrupt.
No, you will cash that check, paid for by my children's labor, and have no remorse. No more than your pathetic bigotry towards large families today.
(Oh, and I assume that you have given back all the money you got from the rest of the taxpayers through your special deductions?)
Social Security is a classic Ponzi scheme. When it was first instituted the elderly and others close to retirement got back far more than they paid in. After many decades of transferring wealth from younger generations to older generations, that's no longer the case. Now virtually everyone who retires and receives Social Security is far worse off than if they'd been able to invest their money privately instead of having it taxed away. Sooner or later Social Security will either go bankrupt or have to be drastically modified to reduce/delay benefits. Any rational person who can do simple arithmetic will not expect Social Security to be there (at least in anything resembling its current form) for his or her retirement 20 or 30 years from now. So don't try to rationalize large families who get taxpayer-financed benefits by pretending that they'll pay it back via Social Security.
I do count myself in the Julian Simon economic camp that believes more human beings are a net benefit for a free-market society, in that they grow the entire economic pie. More hands and brains and technological progress historically do not use up natural resources, they generate more useable resources. Contrary to Malthus, overpopulation is not an inevitable long-range problem. Indeed, the more advanced the society, the more that population tends to stabilize or even decline due to individual choices (i.e., more parents find it advantageous to concentrate their personal time and resources on just a few childeren).
That's why I say I have no problem with people who choose large families. It's not my personal preference, but this is supposed to be a free society. There are advantages and disadvantages to large families, and the overall impact of a somewhat higher population growth rate is more likely to be beneficial rather than harmful.
So have a large family because you enjoy a large family or because you believe that's an important value and if you can afford a large family. Just don't have your large family at my expense, or make me subsidize your preference. If I save money by having fewer kids, that's my money, not yours to take (via government taxation) so you can afford to have more kids. As long as we respect each others' rights and free choices, we can all get along.