The thing you should understand about hypotheticals is they're not a substitute for the equal sign. When I present you with the hypothetical "why make murder illegal," I do not mean to suggest that !(proscribing account sales) = !(proscribing murder). There are, indeed, differences.
The text you have quoted was a response to TL;DR: "account sales are a necessary evil, better than they happen here than elsewhere."
If you feel that account sales are desirable, like gun sales in your example, feel free to explain why.
I don't care about account sales, I care about promoting free trade and open discussion as much as possible. I don't "allow" things because I personally find them desirable, I like them, or approve of them.
It's a general ideological position, this isn't going to change.
There are several other forums where people can go if that's what they want.