Perhaps it's a good thing to incentivize the liquidity providers.
Also, I think you should welcome professional traders and bots, as that is probably the fastest and best way to achieve high volume and liquidity on the exchange. Sure, that will require you to provision extra network/computing capacity and a good API, but I'm pretty sure that cost is easily outweighed by the "services" they provide to regular users.
All liquidity on financial markets is provided by Professionals...
These are highly skilled people that expect to get paid for providing a valuable social service...
That's why being a trader is an honorable profession... unlike, say, being a poker player.
No Pros = No Liquidity = No Exchange...
Also, when the Pros stop trading you have a "liquidity crunch"... and prices crash.
This whole idea that tiered fees "discriminate" against amateurs is juvenile...
It's the other way around... you must have incentives to attract Professionals.