Even if there's a small chance that it would make a difference, wouldn't it be worth it if you have the money and you feel like it's your duty to protect others ? At worst, it's useless and you have contributed to make a vaccine more profitable (which, IIUC is a problem for vaccines ?)

At worst, it's harmful!

From top of my layperson head: bruised insertion sites, tainted needles, tainted vaccine supply, customer capacity crowding for the pharmacy, squeezing supply capacity for actual target demographics, etc etc etc.

Things have tradeoffs, even if they are subtle. Relentless follow-through on marginal protocols should generally be treated with suspicion.

Stranger danger advocates brush off the criticism that most abductions occur among family with the "if there's a small chance it would make a difference" argument, but this ignores the real harms of teaching children to fear everyone by default.