Not surprised at all, I've been using the Internet and writing software for a couple decades now. Heck, I might've written one of the validators you're complaining about. But they are typically written to avoid +, for the exact reasons you described.

For those sites, you can add a dot in your username. Then you can ignore any emails sent to an address without the presence of a dot or a plus.

I'm sure there are sites that don't accept dots either, but I've never run into one. So you have to make an exception? Oh well.

I agree that it's easiest to do with service@domain.tld, like the grandparent suggested.