Some of us should have some nuance when dealing with doomers. Yes, we should keep fighting and keep being optimistic. But before you ignore or dismiss a doomers, ask yourself if he's giving you tactical advice. For example, some posters said that evidence is useless until someone takes action on them. That's a good point. A soldier needs to know any potential pitfalls of his strategy. A soldier can't just unquestionably think that his plan will work.
Just look at what happened to Hilary when she refused to hear bad news about the mid west during the 2016 election. Don't be like her.