NATO have a mandate to operate in Afghanistan, but do not have one for any neighbouring countries.
If anyone makes any incursion into any other country without a UN resolution or an invite to do so, they are acting illegally, they are invading another countries souvreignty and they are disrespecting an ally.
Pakistan have a right to be annoyed. They might get $billions in aid, but that does not mean we can ignore all normal relations and invade another country if we feel like it.
And such disreguard is very counter productive. Every Pakistani is going to be annoyed at such a violation of its territory. Any proud country will not be happy if even an ally or friendly country takes it for granted and carries out operations without its permission.
Rov1100
Read the question, this is about NATO not the US.