[Anguirel]

Well, their attitude isn't "The Ulfings are probably going to be treacherous, therefore we're going to lose the battle, therefore we're all going to die, therefore we should stay away."

Instead, they heroically think

"The Ulfings are probably going to be treacherous, so our lords Maedhros and Maglor are in trouble, so we've got to be there to protect them."

Sam distrusts Gollum, but he still goes with him to protect Frodo. It's that kind of idea.