How do you regard people who insist on only playing White?

They're pussies that are too lazy to learn the game properly (learn how to play a defense properly). Black pieces vs white doesn't even matter for amateurs, in the end the best one will win. If it's an advanced player doing it, then he's mentally a child and needs to be grounded.

They are (perhaps) a bit less likely to lose.

Personally during my time playing over the board tournament games I have had better results with the Black pieces . Once had a 34 game non-losing streak with Black 30 wins 4 draws ... Losing To IM Igor Ivanov on both ends of the Black Streak .

No one good insists on being white so probably a scrub.

It's better to practice with both sides. It's that simple.

Egg whites