The IRS also sends the letters to people that they owe money. This year my accountant didn’t realize I was owed a credit. The IRS mailed me a check and a letter explaining why they adjusted my return and issued the credit.
It's hard to know where to draw the line but you could reasonably argue that chasing low income people for small amounts is net negative societal utility, even when you get them to pay up.
The thing that is often ignored, unknown, or forgotten, is that it doesn’t have to work this way. Some countries send you an end of year report on how much they collected from you and you can audit them as well. It’s less laborious than our system. I am blissfully unaware of the complications of such a system but I’d like to think that it works better. I’d like to think the people of the IRS would prefer that too.