That's why I went out of my way to viciously attack them when the thread was created. What they do is a form of "concern trolling". Concern trolling is a very effective way to demoralize a group of people. Having "allies" show worry and concern makes people feel worried or concerned too; consensus is part of assessing optimism and success.
Concern trolling works so well because it seems indistinguishable from real concerns by actual allies. One way to deal with it is to mock their feigned concern (e.g. "Bad things might happen! Ignore anything good ever happening! Bad person did something good—still bad! Small good thing done—bad, didn't fix the whole problem!"). You can run down the flowchart of possible futures; which often reveals they think a positive outcome is impossible. You can ask them for realistic solutions and fallback plans. You can just bluntly tell them they are being a whiny faggot (depending on the group and context).
Concern trolling is one of the main ways 4chan has been destroyed by shills and bots. Endless infighting about how nothing will ever get better. 4chan's culture of being contrarian makes concern trolling easier. The site owner faciliting the concern trolling dooms 4chan to being a demoralization tarpit.
Authentic negative criticism has remedies, alternatives, fallbacks, and personal preferences. Concern trolls avoid seeing anything positive like a vampire avoids a cross.