A single field breaks fewer names than forced first and last names, though, and is a simpler implementation too. Plus, as long as you accept any input (besides blank, I guess), then the only way it will be broken is during display and at least the user sees the exact name they typed in, exactly how they typed it in.

A single field also breaks the expectation that people do not get called by their full names in every interaction. This is a very common expectation, and violating it makes you sound subtly more like an evil robot.

Is this a lesser offense than mangling a name that doesn't cleanly split into first/last? At the individual scale, probably.

The impact, in aggregate, on UX/sales/utility? Could definitely go either way depending on your userbase.

That's not an evil robot, it's a polite robot.

Better than the slimy feel I get when a robot calls me just by my first name. You're a robot, we're not buddies.