Hm. I may have less knowledge on this than you, so I don't fully understand how exactly this is harming the community. So here is my (maybe naive) perspective and the questions it raises for me:
If vote buying is a bad thing, is Steem buying a bad thing, too? Aren't they a little bit similar in the way that you can either a) earn your Steempower or b) buy it?
I did buy Steem in the beginning. Because I believed in it as an investment, and because it enabled me to give more to others. The higher my SP, the better for the community and every author I upvote.
I could have gone the slow route - earning; or the fast route - buying. I chose the fast route.
When someone buys a vote, they earn Steempower that they might otherwise not have earned. That Steempower benefits everyone they upvote afterwards.
I think it's great that we have a system where we can contribute with time, hard work, or money. Or a combination of it.
I also think it's great that some creative entrepreneurs spotted a niche on how to start a business here in our Steemiverse. I have never bought a vote - I don't need to support them if I don't like them or see no value in them. But people who do see the value, will use them and that is fair. Supply and demand will regulate that.
I also delegated some of my SP recently to @boomerang because I wasn't on Steemit a lot, so I didn't use my upvotes and I thought I was doing a good thing by giving my SP away so that others can use it and benefit from it while I'm gone (and me, too, of course - so far I've always seen the win:win in everything that happens on Steemit).
I get your point about quality - but I also think "quality" is very subjective and we'll never find a consensus on what quality exactly means for everyone.
In regards to trending - here's where I am naive - I never check the trending page. The other day when you told me my post is trending - I didn't know about it :) I only check my feed and the people I'm following and want to read. The trending page is not on my "things to achieve" list :)
If the trending page is supposed to be some kind of proof-of-merit, then bought votes indeed cause confusion, though, and they should appear under promoted, because that's what they are, right? So this part I totally agree with.
For the rest - other than causing confusion and a conflict of values, I don't see (yet) how this economically harms the Steemit platform and community. Based on what I wrote above, I have a feeling it might actually contribute.
I love how passionate you are about Steemit and bring this up to be discussed here. I'm genuinely interested to see all the responses to get a better perspective on this.
I like your way of thinking! Actually you're right: when I power up, I'm also improving my position on the platform through monetary invest.
However, I thought (and maybe I'm completely wrong), that this place was created to give value back to the ones that create value, and that Steem was supposed to be a currency that rewards given attention. Now, if we're able to use vote trading services in order to buy attention (visibility e.g. through a trending position) then we purchase attention but we don't earn it any longer.
My personal understanding of the current content structure is: attention (reading time, social interaction, etc.) has to be earned. That's the driver of this eco-system. At least that was my understanding of Ned Scott's presentation at the first Steemfest in Amsterdam. I wasn't there but I watched the videos. There was one chart where @ned explained steemit's life cycle. The core driver here was value created through social interaction.
Maybe I'm much more naive than you are but that has always been my idea of this platform :-D