Sure, tone galore. But that's not the point, is it? DMs who say no also probably has tone galore, just a different tone than yours.
Put uncharitably, a player of mine who wants to name their PC 'Pikachu' and pet 'Crackejack' is just pissing into the vast sea of verbiage I --as DM-- am the master of. So I let them. It's of no consequence (except making them happier).
But a PC has about a thousand times more screen time than your black magician Dr. Mephisophocles. And the thousandth time my new halfling PC Buttcheek Fartmaster introduces himself to your NPCs, I'd be surprised if you as a DM didn't strangle me, a second before the rest of the group throw me off a high cliff.
But I'll provide an example which I find illustrates my point, and since Oryan77 have given me carte blanche to speak for him, maybe a bit about his position as well.
We have never said "we never accept silly names".
I primarily GM a WFRP campaign. As you might or might not know, one of the features of the game is the outrageously silly faux German names.
These names, in the official setting, are so groaningly bad that German players have been known to change them to less silly German names, because it totally ruined their fun, or even to totally drop the game because the silliness is so off-putting for some German speakers.
At my web site you'll find some NPCs I've made for the game. They have, in some cases, silly faux German names. A doctor named Hilfer ("Helper"), an inn keeper named Uriah Hepp (after the musical entourage), an inventor named Krangelschaft (a nonsense word made up of technobabble), a watch commander named Fengsel ("Prison"), A general named Waffenkammer ("Arsenal"), and so on so forth.
Yes, I use silly names, who would have thought it?
And so do my players. One of the groups of PCs are named Wilhelm, Wilhelm, Wilhelm and Wilhelm. Just for silly sake.
It's immense fun.
Yet, I would veto someone calling their PC's dog "Marshmallow".
Because it doesn't fit the tone, IMO. And my players wouldn't pull a stunt like that, because they know the boundaries and enjoy playing within those boundaries.
I would allow a faux German variant of "Marshmallow", such as Zuckerwurfel ("Sugarcube"), or Sumpfsüßigkeiten ("Swampsweets"), because that's within the boundaries set by the game and by me. It matches the tone.
In another game, I might allow "Marshmallow" or I might disallow it, depending on the tone of the campaign. In a Discworld game, almost anything goes, in a Dark Heresy game as well, mostly. Not in an Ars Magica or Harn game though, because those games have different assumptions and different tones that don't, IMO, lend themselves to silly names.
So, to sum up, there are games and by extension campaigns that I think would suffer from letting players have the freedom to name their PCs silly names, and a DM is well within his rights to say no if the actions of a player will disrupt his game to a large extent.
And the DM is the final judge as to how large that extent is.
/M