Zara and Amazon will also ban you if they see too many returns but as long as you are keeping items than it is fine. They keep track of all orders, part of the cheshbon of offering online sales and free shipping and free returns is that they know that people will buy multiple items in multiple sizes and return most. They save money on the overhead of a store and gain access to customers who otherwise would not shop there.
There are better ways to make a return policy than to make a blanket policy painting a whole community. What the company should do is ban the abusers of the policy which I imagine are a few individuals that are known to the company.