Alright fine.
But still, the resources are going. In their eyes, they are slowly dying. Eventually, it will all be gone and everyone will be screwed.
They see the other option as go out into the world to see what is left. And see if they can find anything, something for them to live off. Instead of staying on the Ark and dying. And living in poverty while the founders hoard the water.
But, heading out takes away a huge chunk of the few resources they have.
Perhaps only 100 people survive. Maybe no one survives. Should they take that risk or rather stay were they are and hang on as long as possible. That is the big question. That's what they're fighting for.
Stay = Security
Leave = Resistance
You don't know what would happen in either case. It's the same in the real world: conservatives rather "stay" where they are (They don't want huge changes, they dislike change) while progressives try to get forward (They try new things). It's comparable to the resistance and the security.