To me, using default face emoji gives off the same kind of vibe as still having the setting that adds "Sent from my iPhone" to the footers of your emails enabled. Or driving around a car you've purchased with the car dealership branding badges and license plate covers on it. Or using a laptop with all the factory stickers still on it. It signals a kind of "this is fine" lack of care or concern by allowing your own expression to be polluted by pre-canned expressions from a corporation.

Counterpoint: "self-expression" through more consumerist markers is no less bullshit. I don't care about your lifestyle brand and I would, if anything, respect someone more for not paying extra to try to give the affect of being a special little guy when all they are doing is displaying a different flavor of corporate bullshit messaging.

Express yourself in word and deed, not shit you bought.