Although downvotes don't help provide feedback to the users, allowing them can provide an immense amount of feedback for the operators of the community.
You need a certain amount of positive feedback relative to negative feedback, and if you monitor that ratio, you can have a good pulse on the quality of your community. If you are not maintaining a high ratio of positive to negative feedback, you can take action to increase positive feedback in meaningful ways. You can also use provided negative feedback to tailor interactions. Someone downvotes a particular thread? Don't notify them of any future discussion on that thread if you otherwise would have, etc...
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Although downvotes don't help provide feedback to the users, allowing them can provide an immense amount of feedback for the operators of the community.
You need a certain amount of positive feedback relative to negative feedback, and if you monitor that ratio, you can have a good pulse on the quality of your community. If you are not maintaining a high ratio of positive to negative feedback, you can take action to increase positive feedback in meaningful ways. You can also use provided negative feedback to tailor interactions. Someone downvotes a particular thread? Don't notify them of any future discussion on that thread if you otherwise would have, etc...
See: https://en.wikipedia.org/wiki/Critical_positivity_ratio In my opinion this ratio applies equally as well in social networks and online communities.