We could learn a lot about how zombie-ism is transferred (everyone's been scratched so far, not bitten), and possibly be introduced to the idea of immunity, which could lead them towards a cure. Also, maybe we'll find out more about Ravi's past? He did say he was fired from the CDC, after all…

Didn't stop Daredevil.

Except the grounder group we see is actually an alliance of 12 nations. They will band together if it makes the most sense, and have a history of it, especially under Lexa's leadership. I think you're confusing the grounders with the Mountain Men in this case - the grounders would be willing to ally, they just want…

I always thought it wasn't the people they were saving inside that mattered most, but rather getting rid of the Mountain Men once and for all to save hundreds, thousands, or even millions of grounders in the future.