Unfortunately.. yes there is a harm in that in the long run. You see.. all the use of these anti-bacterial this and anti-microbial that.. will eventually.. create 'superbugs' that are resistant to those items which currently do a great job of killing them.
We've seen this in hospitals to a degree with infections that are extremely resistant to both anti-biotics AND the typical cleaners used to kill them.
TV does a great job of grossing us out with multi colored images of germs on phones, soap pumps and whatever else.. but good grief. WHY do I care if the soap pump has germs on it?? I'm about to wash my hands within seconds of touching it. And the Johnson & Johnson's and Proctor & Gamble's of the world do a great job of creating a market for sprays, wipes, soaps and even furniture waxes (yes furniture waxes) that kill 99% of live bacteria in lab tests.
Unfortunately, few of us use the techniques they used in the lab to clean our home/hotel room/child's toys etc.
I find the whole thing a touch ridiculous.
Anyway.. maybe not tomorrow.. but the continued and widespread use of these things WILL create "super" bacteria that aren't going to die easily. I'm not a doctor or a nurse, but I do realize that this is how these things work.
That's the harm.
Long story short.. they are washed every 'few' guests is my guess. That means not typically between EVERY stay.
If you have concerns about the bedspread, call housekeeping and they will bring you a clean one.