What did you want him to do? Talk more? If you had a problem with him not speaking, then that's one thing. That does not however mean he didn't do anything, because he did! If that's not it then I just don't get your point, I'm sorry.
He was with chief to protect earth (mostly because Truth was on Earth) and when they we're on the ark his goals were kill Truth, and stop the flood on Installation 4B. Stopping the flood, and killing your most hated enemy is no good reason?