Horrid, horrid things. And the bumper's been drilled by a 4 yearold on a pogo stick by the looks of it...
And he was using a blunt spoon to make the holes.
This is why I don't like screwed/bolted on plastic plates on modern cars. Wide, double sided trim tape is the way to do it. Quick, cheap and easy. If you clean the surfaces effectively(quick squirt of brake/carb cleaner or acetone will do the job), you have to really want them to come off. Looking around, very few people pay any attention to where the screws go/line up and just look dreadful. And that's before they go rusty.
When using pressed aluminium plates on an older car, I do tend to bolt them on as they're often just hung under the bumper; but then I use the same polished button headed stainless steel screws that I use everywhere else for non-critical items. And that goes into a properly set rivnut as self tapping screws are an abomination.