The plot comes in Arcs, every Arc can be failed or completed, but Seeker will keep things in check for sheer stupidity such as what had happened. Clearly by Bruce's remark he knew who they were, had it been a low INT character it would be understand that they didn't understand and instead shot. Someone with decent intelligence and a tag in speech should understand how words work and he was an ally that offered to take them along. Trying to simply kill the person that was obviously on their side and trying to get them away was a dumb move, and could have killed the entire team in the process. He is the only way this continues as they've already chosen to press on instead of retreating, thee's no going back. If Seeker didn't intervene, everyone probably dies, and when everyone dies it's hard to find the inspiration to go back and try again with everyone. This was absolutely critical, and therefore he stepped in as he should. There's still a chance Bruce, or anyone and everyone will die, but it's no longer almost guaranteed.