I would really like to know what is unethical (or even illegal) about this (just so I can understand this correctly).

Uber

* created multiple fake accounts on lyft to know about it's drivers

* figured out that it's drivers were assigned numerical ids

* used said ids, to track lyft drivers.

imho, this is just figuring out your competition (say by signing up to the service) and then using this knowledge to improve your service (by incising drivers on both platforms to ditch one).

This is one of those "do things that don't scale" mean (or my interpretation of it). I say this because, one multi-billion $ "startup" is doing this to another multi-billion $ "startup".

Also, I'm sure this would never be an issue if Uber was not in the press for other crappy stuff they did.