OK, I understand. Thanks for the suggestions.
As you pointed out, the first option can be mostly circumvented by having multiple accounts, but in any case, there are significant stakeholders who are strong proponents of downvoting and who actually want to dramatically increase the amount of power the SP provides people to downvote. I disagree with this approach completely and I doubt it will happen - but it highights that there is a possibility that changes to this system would be highly controversial and destabilising.

In the case of malicious downvoting, in some cases communication might help - but I think that in most cases it wouldn't.

Downvotes are really the main mechanism the community has against real spam, so limiting the downvote effect on hiding posts does present a real problem in that sense.. However, it perhaps comes down to a balance of how much of a problem the spam is vs. how much of a problem malicious downvoting is.

I agree on the need to eliminate the effects of bid bots - I have presented options for that, but the larger stakeholders that did speak out tended to favour increasing the power of downvoting as a counter to bidbots. I see this mostly as an attempt to increase their own personal power, rather than as something genuinely intended to help network wide.

I am not really aware of any way to prevent automated downvoting on a technical level. Downvoting could have a longer time delay built in, but it is not possible to stop bots from downvoting currently.

I agree about the hiding of posts to some extent, yes - I have spoken about it before.

Any form of arbitration on Steem is unlikely to succeed due to lack of organisation at this point. Steem doesn't even have a marketing team, let alone anything that can be relied on for arbitration. What happens if the arbitration team is bribed? How is this checked? Such a system is inherently in opposition to the principle of anarchy, but then so too is economic hierarchy itself!

The only idea I have to offer that is straight forward and that is a definite one that can be achieved, is for dApp operators to include a downvote area in their website so that we can all see who is being downvoted. It would be useful to have a text field that records the reason too. That way, the community can monitor malicious abuse of the system and act accordingly. I suggested this over a year ago, but change is slow around here!