That is really dumb, borderline retarded decision in my opinion.
Why is it retarded ? Because game massively incentivizes to buy gold already, therefore incentive X to buy gold is okay, incentive Y to buy gold is not okay, because we said so is dumb reasoning.
Here are some more incentives to buy gold: Epic mount. Craftable gear. Fucking flasks. Consumables for raiding. Everything is fucking expensive. I dont know what kind of person would farm for mount, craftables, consumables etc, but then see GDKP runs and go buy gold. Im sure ANYTHING that costs gold increases chances of someone thinking buying gold is a good idea, but CMON, you have fucking twinstar character auctions where every ****** can buy farming character for him for real money.
GDKP runs are for rich fucking alts, i know most people from most top guilds play fucking 5 characters at once and have banks with few thousand gold or more. So if that guy wants to buy BRE on his warrior NR.3, thats somehow wrong ?
Its like, group of players come together and want to do something FUN together, that exists on blizzard servers, harms no one, and is completely within game rules, and you kill it. Just because. 'We dont think thats a good idea', gee, thanks mom.
If GDKP runs are shit, no one will join, if people want them and will join them, why would you not allow them?
I would understand if they were going on FOR A WHILE, and you saw actual big increase in gold buying/selling/botting and then banned them, or shared actual information/data how you arrived on that conclusion that gdkp will severely affect gold buying/selling. Maybe you have very very good reasons, but you are not presenting reasons, just decision.