Thanks for the explanatory link - guessing this US government initiative was well-buried on Google UK.
You've educated me, as I thought there was next to no social provision in the US for people on low incomes; it's good to know there is something even in the Trump regime!
I'm not sure of its relevance to begrudging UK taxes going to the Royal Family, though. I'm a dyed in the wool Labour voter, which, loosely speaking in UK parlance means I am pro- my taxes going to people who don't have much money, and anti- them going to people who are already rich (e.g. The Royal Family).
Not sure if it's under the same name, but see my post a few days ago about the Tory plans to replace PIP (a UK disability benefit) with vouchers - this sounds a bit like the SNAP card, and this element of 'policing' how social security benefits are spent is precisely why I'm urging people to vote Labour in the upcoming G.E. - so that benefits continue to be paid in cash.
I begrudge a single penny of my taxes going to the Royal Family precisely because I want them to go to people who actually need them - people living in poverty. And if people want to spend their benefits on (e.g) fags and booze, I would hardly begrudge them as a drinker/smoker myself.
I hope @BemusedAmerican that I have gone some way to un-bemusing you about the nuances of left wing/right wing attitudes to tax in the UK.
TLDR - the sort of person who is happy for their taxes to go to the already rich Royal Family is more likely to begrudge a birthday cake put on the SNAP card than the sort of person who doesn't want their taxes to go to the Royal Family, but to people in need.