You may disagree with the net effect of the decision, but the decision is not hard to understand. The people that are doing it are placing a larger value on harming Reddit as a platform to hopefully force corrective change or encourage movement to competing platforms. You place a larger value on preserving knowledge.

You say you get pissed. My question is do you get pissed at the person who deleted it, or do you get pissed at Reddit for alienating it’s own users to the point of deleting their own comments?