1) The point about letting the trolls grieve and doing anything else would make the Alliance like the Horde is made by Jaina, not Anduin. He just agrees.
2) Using troops as a distraction is a very standard military move and usually results in those troops dying. It's not great, but that is how warfare works. You can value as soldiers life, but you need to be able to sacrifice it too. In this case the troops were even fully aware of it and volunteered. This would rarely be the case in reality.
3) The entire war was started by Sylvanas. Anduin is not in this war to be the agressor or wipe the Horde out, he is defending his people and wants justice for the Banshee's crimes. The Horde could have immediatedly turned on her after the horrific genocide of Teldrassil, but instead they decided that it might be fun to follow the mass murderer. All lives lost in this war are the fault of Sylvanas and the Horde, no one else.