If a user is on a metered connection, and "seeding" Windows updates pushes them over their bandwidth cap, then MS is quite literally stealing from them.
I'd say that's an excellent example of a question of ethics.
That scenario would never happen since P2P updates (a.k.a delivery optimization) won't use metered connections [1].
[1] http://windows.microsoft.com/en-gb/windows-10/windows-update...
"If you use a WiFi connection that is metered or capped, make sure that you identify it as a metered connection."
The behavior is opt-out: you have to tell Windows you're on a metered connection. Or did you think it would somehow figure that out on its own?
Even if it only messed up and misidentified a connection as non-metered one time ever, you'd still be pissed off if it was you and it ended up costing you real money.
[1] http://windows.microsoft.com/en-gb/windows-8/metered-interne...