Do downvotes have a disproportionate effect or something?

No. Stake based; Hive Power (HP). More HP equates to more 'say' in where rewards go. The reward pool is shared with everyone and maintained by stakeholders. Even if you have 1HP in your account, you are a stakeholder, with minimum impact. And with the combination of voting power (VP) and voting mana (VM) one can hand out far more effective upvotes than downvotes.

With this scenario seen above (the post), I didn't feel it was necessary to 'reward' that behavior. With my stake currently, my votes in either direction at full VP are worth roughly $1.70. If others felt the behavior seen above should be rewarded, they can counter that downvote of mine, easily. More of them, than me.