As mentioned in the whitepaper:
Every day the reward pool is distributed among all post, according to the upvotes.
If you take a huge chunk, there is less for the others.
You are also taking a part of the reward pool that is in no proportion to the content you provide.

On steem, as there is no police, everyone has to decide for themselves, what's ok and what not.
In my humble opinion, the use of bidbots beyond a payout of 50 is not ok; also people notice this and take you less seriously.
The fairest way is to constantly provide good content, maybe invest 5-10 steem here and there for bidbots, be consistent and patient.
Greed's the biggest killer of all.

btw.: As you said, you pay for it. The profit goes to bidbots.