Such organisations are fairly unique in that they are involved in the sale of products which they have never seen (and could never hope to see all of them) and are hence reliant upon product descriptions and/or photos provided by the sellers.
Not good enough.
They are running a business of providing those sales channels.
They are making money by providing those sales channels.
They must be held responsible for what those sales channels are used for, and if they really cannot control the use of something they provide and they profit from then yes, shut it down.
Trust me - they would soon find a way.
If initiatives result in, say, increasing number of eBay listings being removed, one fears that this could result in sellers (certainly 'commercial' ones) becoming much more clever in making sure that the dangerous nature of their products cannot be determined from the description and/or photos - which would mean that even those of us 'in the know', let alone the public in general, would not be able to determine which of the products were more likely to be safe to buy.
Maybe it would be no bad thing if eBay went back to being a place where private individuals buy and sell - get rid of all businesses using it.