This is an argument I've seen floating around OV and other blogging sites almost constantly. There are people literally arguing that gays shouldn't be allowed to marry (civilly, not religiously, I don't care if religious institutions don't want to preside over gay marriages or not, that's their choice) simply because they can't reproduce.
So not being able to reproduce gives you an excuse to automatically throw them into having to pay higher taxes? Not being able to reproduce means that they their partners shouldn't be allowed hospital visitation rights because they aren't "immediate family?" Not being able to reproduce means that they shouldn't be allowed to will their partner their estate?
OK then, I guess I shouldn't be allowed to marry, because I can't reproduce, since I have no children and have had a vasectomy. Being surgically sterilized or naturally sterile I guess is also a good reason to prevent people from getting married. Seriously?
If you understand the ridiculousness of that argument, then you can understand the ridiculousness of the former.