Hello @kelvinwong, glad i came accross this post. I for one does not support vote buying and have never used the services since my few months on steemit. Reason been that i dont see it as profitable and the effect it has on visibilty is feasible to me.
However, i can understand why people would want to buy votes. It can be very fustrating and discouraging to have put up a post and do not get rewards. Lots of  steemit accounts are dead at the moment due to posting and not get rewarded. Now there is a glitched to what is know as quality post on steemit. Long, well disseted, with good pictures, for a post to be quality enough to get reward. Not everyone can do that. Like @donkeypong pointed out, other forms of posts needs to be rewarded also. When i joined steemit, i thought it was a place where you can just blog and be cool. But thats not the case, it is about who likes what you blog, is about who gets to see your post, it is about what steemit regard as a good content. I do understand that, as we cant really be visible to everyone, or get to reach everyone. 
I guess this is the reason people have to opt for vote buying to encourage themselves to blog. The truth is we all have our circle on steemit and cannot reach every good content. However quality the content of a minnow post is, they can never get what a whale gets for reward, not because the content not good enough, but the circle he/she belongs to. 
Buying votes may be bribery, but people have to do what they have to do to earn, build a reputaion, survive and be consistence on steemit. Despite the fact that, few of the many powerful people have been very helpful with rewarding, they cannot reach everyone. 
In this plight i would suggest, in as much as buying of vote doesnt give much value and tends more to the abusing side, buying of votes shouldnt be frowned. For those who needs it, they should be able to access the services,if that is what it takes for them to earn and remain active.
My sincere opinion. Thank you.