Are you kidding?
I'm sorry, but a student is not a professional, and professionals are the ones who are paid. What ever happened to gaining experience?
There used to be this thing called an Apprenticeship where you studied alongside the Master, learning the trade, and then setting out on your own.
I think it sets a bad precedent convincing people to charge for something for which they may not yet be qualified for.
No, I am not kidding...
The problem with working for free to get experience is you only get crappy experiences...
Professional is a tough word.. when it comes to design, it takes a *lot* more than simply getting paid for me to consider someone a professional designer.
Students today still "apprentice" via internships with design companies and corporations, but that is very different than doing a freelance project for free... but understand that very few internships are unpaid now... most students are paid at a reduced rate: 8 - 15/hour. The idea that you have to work as an indentured servant to get into the business has passed. Even the very competitive and desirable internships (ad agencies, etc) have some sort of financial incentive. Frankly, most students today cannot afford to spend a chunk of their week working and not get paid in some way.
I don't understand your last argument. If a student (or anyone) has created a design that is "good enough" for the client to use, why is it not worth paying for? If they are "not qualified", the work should not be used and they should not get paid. No-one is getting fooled here, and no-ones labors go unrewarded.
Design students do plenty of work for free... their schoolwork, which is designed to give them a measure of experience in both the visual and professional aspects of design. The difference is the only people who benefit from all that free labor is the students themselves. When they are ready (usually after two or three years of dedicated study) the students begin to intern and, if they choose, take on freelance work.
Every design student who leaves my program has 4 years of study in visual form and color, 3 years of study in typography, 1 year of information design, information architecture and interface/user experience design, and has spent 4 months personally captaining a professional-scale design project. They are comfortable working alone in a team, know the Adobe creative suite including After Effects, can program either in Java or AS3, and have one semester working in HTML5/CSS3/jquery. In this context, I have no issues with them asking for a bit of money (they don't charge "professional" rates) for their time, and I hear very little complaints from the people they work for.
