I think a bunch of people are going to die, yes. I also think, like a lot of experts who have studied the issue, that action now will produce effective results from among some different possibilities, not all of which are extinction. There's still a potentially drastic reduction in the level of horror that's involved in the outcome, largely because the outcomes at the bad ends of the possibilities are so, so bad.
That's why I use the example of the zombie movie. You're trying to argue that because the situation is horrible (which, yes, it is), it's okay to resign yourself and everyone else to an even more horrible future, and you're actively trying to discourage people who are trying to at least do what they can. I think that's a stupid and counterproductive thing to do.