Ugh. I really think this logic is convoluted. I hear this response all the time trying to justify seed prices and it annoys me.
First of all, not everyone that grows weed sells weed. Some people just grow for themselves. Some people grow for patients. Some people have no means of recovering costs, so prices matter. There are also a lot of sick folks, on fixed incomes that grow this plant to help their ailment, and every penny matters.
Second, why should someone pay any more for anything related to their grow than they have to? Would you go to a hydro shop and pay $50 for a bag of soil when another shop right up the road carries the same soil for $25 a bag? What about nutrients? Would you pay $200 for nutrients when you can get them for $100? Electricity? Has the thought ever crossed your mind to call up your electric company and ask them to start charging you double? No, you haven't, because that would be stupid.... just like it would be stupid to pay twice as much for a pack of seeds that you can find elsewhere for half the price.