No, thank you.
What if you start PvP with one faction and you don't actually enjoy that faction and decide you'd rather PvP with another one?No from me too. I have 10 AD characters (only the first on ever set foot in Cyro because I do not really enjoy pvp) and recently created one character in each of the other factions just to be able to buy the specific alliance style stones form the Tel Var vendor. With your proposal, I would no longer be able to buy the DC and EP style stones to get armour crafted with them. Yeah, no thanks.
Yeah. It's not like you could sell the AD ones and buy the DC EP ones from a guild trader. This is definitely the smartest reason to reject alliance enforcement.
What, give money to an enemy player? The ones that kill me when I try to do some Cyro questing? No way. I created characters in the enemy factions precisely to avoid it.
No? Guild stores are multi-alliance. Someone from AD could have bought DC EP style materials and decided they don't want them anymore.
...have you actually bought Alliance style stones from the siege merchants?