But they might be horrible old harridens. And their husbands might be historical rapists. I might not want my taxes being used to keep their feet warm. And other pointless arguments...
We exist as a society. If your house is burgled, or you are mugged and you ring the police, we don't say "well, it didn't happen to me, and you should've double locked all your doors and never gone out, and anyway, where is your dad from?
If you or your offspring turn up at A&E because you had an avoidable accident, we don't ask where your great granny was from.
It's a nonsense argument. People use "well you put 'em up then" as a conversation stopper. Like a 'gotcha' if you like. It's a way of derailing any reasoned debate. A bit like "well, you smell of poo"
And anyway, you have no way of knowing which pensioners are British.