There is a very good way to avoid sending random merits, not to be greedy, and not to accumulate many merits. If you, OP, were more generous, then sending twenty-two merits at a time would be impossible. Such situations will never happen to people who do not accumulate their merits. Except for everything, don't be sorry; just please the person who got such a gift.
I don't remember having had 22 merits to send out, maybe when the merit system started and we had airdropped merits (I don't remember how many), but other than that I don't think I've even come close to accumulating 22 smerits. I'm sending them as they come along.
Some months ago, I was doubting whether to send 2 or 1 sMerits to a given post, and ended up sending 21. It happens every now and then.
As said, I think this happens to those who hoard merits and those of you who have a lot of smerits (top merit earners+merit sources). It doesn't happen to us commoners.
As the sender of tens of thousands of Merits, I'd hate to see a confirmation pop-up. Once you're used to it, you'll click it without reading, so all it does is waste your time.
I've made mistakes a few times, but in total it's about 0.2% of my sMerit that went wrong. It's not a big deal.
I agree, looking for a solution for such a low error rate does not seem worthwhile.