Why? The rules part do not mention anything of fireball or collateral damage. The rules only say that creature in an area take X fire damage. And when again following Balesir's argument from Post 282 just because the Power is named Mocking insult it doesn't mean that an insult is invloved.
Again, incorrect. The rules, as I have spelled out references to no less than FOUR times now in this thread, do specify that there may be collateral damage (in the case of fireball). DM's discretion. Just like every other edition.
So why would a fireball be a ball of fire? The player can simply describe that all enemies in that area simply burn from within.
So either the player can change on a whim the description of the powers, which means a fireball is not a fireball anymore and thus flavor doesn't matter or the player can't change the nature of the fireball no matter how he describes it, contradicting your previous statements, and we are back to 4E allowing skelettons to be mocked to destruction.
A fireball is a ball of fire. An Arcane attack with the Fire keyword. Whether it only hits creatures or burns the whole dungeon to ashes, is, like I said, up to DM discretion, just like every other edition.
If the players and DM have a social contract at their game that says that how they describe their powers affects how the DM will make judgement calls, then fine. If not, then it's entirely in the DM's hands, just like always.
No matter how many times I point out to you that your grasp of the rules of 4e are less than firm, you keep arguing with me. I get that you don't like 4e, or its style of narration, and that's just ducky with me. I couldn't care less, to he honest.
If you find it so objectionable, and don't want to see such things in 5e, my suggestion to you is, go write to WotC, and tell them what you think. Vote in Monte's polls. Make your voice heard.
And if you don't care what happens in 5e, and are content to just keep playing 3.x or PF, or AD&D, or whatever - keep on doing what you love. There is no need to just argue for the sake of arguing.
The arguments I've heard so far are hardly compelling enough to make me have some kind of epiphany and decide that suddenly I've been having BadWrongFun all these years.
EDIT:
When someone says to you "Do it however you want", do you get the impression that it matters to them?
When you ask someone how you should do something and they answer "However you want", do you think it is important how you do it?
When you ask someone "How should it look like?" and they answer "However you want", do you get the impression that it is important?
When a power says "Ranged 10, single target, CHA v WILL; on a hit, 1d6 + CHA mod -2 to hit rolls, make it look however you want", is the look of it important?
It matters to me. It's important to me. In fact, I relish the opportunity to make my own flavour text. It's one of those things that keeps me engaged in fiction of the game. Clearly, YMMV. And that's fine. Like I said above, if you have an issue with this, complain to WotC. If you never intend to play a hypothetical 5e, go play the way you want, and let others do the same. Neither one of us is Wrong.