Think the reasonings are that once the public generally accepts the concept of a store where cosmetic gear can be bought, that blizzard would slowly shift their development of the game to accommodate store sales. What once would had been just added to the game and obtainable in normal ways, they could just add it outside or even shift some issues to premium store goods (for example the lesser charms, xp flask). Why balance it directly in-game (by increasing lesser charm drops, or reducing the amount even further, why not add such a flask also as a heirloom) while you can just put it in the store? In the case of the xp flask: while it is in the game why hunt and camp for a rare with low drop chance if you can just use a credit-card? Another example is the declining quality and/or uniqueness of the mount drops in raids comparing WOTLK and the expansions thereafter since the store shop. By directly buying the items in the store they see this as a support, a greenlight for blizzard to slowly shift their way into micro-transactions: no longer would micro transactions be build around the game, but the game be developed/build around micro transactions. There is absolutely no guaranty that the profit will be partially used for improved content development, if at all. It will be used to please share-holders especially after Vivendi failed to sell Acti-Bliz (which was stated in a news press that they are looking for other ways to...compensate the loss)
This leads to the next part then, why would someone care if someone buys /approves the in-game cash shop, it would not affect them in any way. Well, if people invested so much time already that an emotional bond is formed (and with that I mean years) and see that the developer is shifting the game towards a direction that would ruin all that, of course they would see any supporting that shift as an affront to their enjoyment of the game. They would take any actions even if it means denying others of their enjoyment. Is it petty or bad taste? That depends on the eye of the beholder and/or the majority what is deemed acceptable as with all things in life. In case of those vote-kicks apparently the majority voted yes when the kick went through.
But bet this post gets ignored like other reasonings and the entire topic being reduced to boo-hissing and throwing mud at each other, reducing the arguments to surface level.