But what will happen to the random guy that invested more than he can lose @ 20$?
That person will learn a valuable, albeit painful, lesson and hopefully will not repeat that mistake in the future.
How many people spend $20 on cigarettes, or a horse race, or a bottle of whiskey?
All these are more of a "mistake" than an investment with a possibility/probability of making a profit. You can't be worried about other people's decisions.