Was it out of character?

[the phantom]

The scene would have been so much more powerful (in my view) if, after saying his piece, the Mouth had simply turned round and ridden back to Mordor. Aragorn could then have done his "I will not believe it" bit and ridden back to give his inspiring speech. It should be "Hope against all odds", not "Silly old Mouth - I'll just chop off his head and that's that".

Yes, I totally agree with that.

when the good guys start playing by the rules of the bad guys, then they are no better than them

I've always disliked this notion. I'm sorry, but when you're dealing with someone who is without a doubt evil and horrible and has acted so in the past and will continue to act so- they have forfeited all rights to be treated like a human being.

Now, in the real world it is difficult to define someone as the embodiment of evil, but in Middle Earth there was no doubt about Sauron, the Nazgul, and tMoS. They were sub-human.