sin of joy

12 And in that day did the Lord God of hosts call to weeping, and to mourning, and to baldness, and to girding with sackcloth:
13 And behold joy and gladness, slaying oxen, and killing sheep, eating flesh, and drinking wine: let us eat and drink; for to morrow we shall die.
14 And it was revealed in mine ears by the Lord of hosts, Surely this iniquity shall not be purged from you till ye die, saith the Lord God of hosts.

Why was joy considered iniquity? After all Jesus said:
John 15:11 These things have I spoken unto you, that my joy might remain in you, and that your joy might be full.

And Paul similarly:
2Cor. 2:3 My joy is the joy of you all.

Could there be a deeper meaning for God's rebuke, rather than just a superficial reading saying that God was unhappy because of some abritrary sinfulness some apply to joy and gladness, slaying oxen, and killing sheep, eating flesh, and drinking wine?

I think that joy itself is not considered iniquity unless it is connected to sinful attitudes. Also, I don't think it is only a superficial reading to say that God was unhappy because people were joyful and glad by killing animals for Isaiah 66:3 says that to kill an ox is like killing a man:

Is. 66:3 "He that killeth an ox is as if he slew a man; he that sacrificeth a lamb, as if he cut off a dog’s neck; he that offereth an oblation, as if he offered swine’s blood; he that burneth incense, as if he blessed an idol. Yea, they have chosen their own ways, and their soul delighteth in their abominations."

Also, there is a connection of multiple sins being described in verse 13, then it is not only because of the slaying of animals. Men were living without the sense of cause and effect since they did not care about the day of tomorrow. So it is today.

So the connection between their activities is "llet us say and drink for tomorrow we die" it does not say that they had joy in killing animals but that both joy and killing and eating and drinking were all the result of their attitude to life.. In Isaiah 63 it mentions God's view of their oblation (offerings and sacrificial rites) as though they were disgusting yet God required them to make these sacrifices. So there is nothing inherently wrong in the offerings but the attitude they did it with determined whether or not it was acceptable.

I guess I hear people trying to condemn flesh eating and wine drinking through this verse and I think that is superficial because by the same token you would have to condemn joy and gladness if you apply condemnation to the others arbitrarily..

It's the attitude not necessarily the action that is the problem here. The attitude is eat and drink for tomorrow we die. You said the attitude means living without reasoning cause to effect and while I agree that it certainly is a characteristic of their attitude it might not be the full concept.

Can you elaborate on this principle?

A lot of people live by this method where they drink and eat as they may die tomorrow. It a attitude about them self, live in that moment.