"...his spam is hidden..."

Muting is all that is necessary for that. That also avoids the following.

"...spamming with their downvotes, proving that they can be abused just as easily as upvotes."

However...

"They think that they deserve everyone's attention..."

Absent downvotes the market will avail creators such attention as they actually merit by the subjective choice of the market to either upvote their content or not. The abuse potential, and actual severe harms DV's have inflicted on the platform, seem not to be necessary to combat spam from your considered reply, for which I am grateful. However, DV's, or some similar mechanism, do seem necessary to combat plagiarism, circle jerks, and similar scams that seek to abuse the rewards system. This suggests to me that restricting taxation (DV's) to those specific purposes is a reasonable policy.

Thank you.