It's mildly dishonest, but it does help you as the employer get closer to the ideal fit for the position. Especially one that is likely posted to a public forum.

The fact that candidates that pre-select themselves out of being chosen is not really a big concern. Why should it be? The way around this is knowing exactly who it is you want for the job, but in that case I wouldn't be posting the job in a public forum. It's kind of what recruiters are intended for.