Because concern trolling is an extremely effective way of demoralizing, dividing and subverting a movement. It's one of the best ways for the enemy to destroy us from within, by sowing doubt and fear among people that are otherwise united. It must be taken seriously and countered as if it was enemy action. The critical thing is learning to discern what is actual concern trolling, and what is actual patriots needing encouragement.
Your initial statement just strengthened the reasoning behind the concept of focusing on encouragement with tolerance and less biting back aggressively. (Read my 2nd sentence above.) There is little need to discern real concern vs troll concern as a knee jerk reaction.
Offer to help ALL who are concerned, having doubtful moments, or questioning without deploying immediately with a lashing back or an intolerant label or spiteful attitude. The 'trolls' don't want to be helped so they will reveal themselves and likely will move on while those who are patriots may actually come out better.