Stipulating active employment as a qualifying criterion does make some sense. In the current climate, someone who already has a job but is looking for a new one can be perceived as demonstrating ambition, imagination, and a willingness to take risks, all qualities that are attractive to employers. On the other hand, it disregards the global picture. Whether they do so openly or not, companies who consider hiring only the already employed are helping neither the economy nor themselves, since they are not doing anything to reduce the unemployment statistics and are just setting themselves up to be inundated yet again the next time they advertise a vacancy; not to mention the negative impact on other companies whose employees they are enticing away.
There are other, more subtle ways in which hirers discriminate. Some of them are legitimate: It's perfectly reasonable, for example, if a law firm looking for a new partner states in their ad that applicants ought to have trial experience. Some are more dubious. If a recruiter calls you and you don’t answer the phone, that in itself can be enough to disqualify you from consideration, even if you immediately call back. You can even find yourself out of the running for an unskilled, entry-level position in retail or fast food on the grounds that you lack experience in those industries. It's impossible to quantify how many good people employers miss out on by pursuing arbitrary hiring policies, but the fact that there are are millions of highly-skilled, highly-qualified folks still languishing on the unemployment line suggests that it's a lot.
The discrimination provision in the jobs bill has been broadly welcomed, although Obama's customary critics have had little to say on the subject. Opposition to it, and to anti-discrimination legislation in general, has been from two camps. There are, as mentioned, those who are concerned about frivolous torts. These lawsuits are typically portrayed as an enormous drain on the economy, although the actual numbers don't support their claim and they rarely bother to provide any evidence that the suits they complain about actually are frivolous other than that they say so.