downvotes are used to mark something as contraversial, each five downvotes cause a flag for said post. personal disagreement i would say is not a valid reason to in my opinion.

example post topic title: "oranges"

if someone says they like oranges and you dont, a downvote is not saying "ahhh i dont like oranges" its more saying "liking oranges is contraversial"

said point is supported by the fact even a single downvote causes a post under your profle to go under the "contaversial" tab- if you disagree, if suggest you either reply a disagreement or just ignore it :)

this is not directed, this is just a clarification and an example stating the importance of a downvote.