It may not be a good
PR but it is their right and it makes sense. They don't OWE anyone anything.
Think about it. When a company downsizes, do they lay off their best people? Of course not. They typically let go the people they can do without.
That pollutes the unemployed field.
There are plenty of good, quality, productive people in the unemployment lines but there are even more people there who are unemployed because of performance or personal issues.
An HR department is reponsible for screening prospective employees in an effort to get the best possible people. That aint easy.
In a market like today's where there are thousands of applicants for even the most basic job, it is a daunting task to try and weed through al those applications. Thier strategy, while distasteful, is probably very practical and effective.
Those who have had to go through the hiring process and screen applicants will understand.
People lying on their applications, people lying during interviews, people saying they's never been convicted when their police record shows three felony convictions, people applying for a job that handles finances when their personal credit rating is as bad as one can possibly get, etc.
Like I said before, the company doesn't owe anyone anything.
EDIT: Dave L hit on a very important point above: unemployed people can be desperate and willing to take any job no matter what. As soon as something better comes along, boom they are gone.
A huge mistake in business is hiring someone to do a job they are not really suited for. It rarely works out. So if you hire a marketing guy to do a maintenance job, he won't be happy, he wont be motivated, he probably won't be sucessfull.