Creating a platform that can be used to buy/sell illegal goods shouldn't be against the law IMO. Are car manufacturers thrown in jail when someone drives their product when drunk?
It boils down to intent. If you intend to make a legitimate platform for commerce that also happens to be used for illegal stuff, (Craigslist, for example) you're in the clear as long as you aren't actively aiding them.
In contrast, if you set up your platform with the explicit intention of selling illegal goods, then you're in trouble.