It's certainly poor style, if not actually wrong, to join independent clauses with a comma when a semicolon or other punctuation would have sufficed. But interjections are usually offset from other clauses by commas, as in:
Dang, what do we do now?
It seems to me that this naturally applies to certain longer phrases, such as:
I don't know, what do we do?
In which "I don't know" functions as a single interjectory unit. According to usual style, that comma ought to be replaced, but to replace it subtly changes the pacing of the sentence, doesn't it? So, does a comma used in this fashion count as a splice or not?
- I'm sorry, who are you?
- What the heck, you only live once.
- You're welcome, it was my pleasure.
- I'm sorry about that, what can I do?
- What the heck is going on, these zombies are ruining my earlier example.
- You are of course very welcome, I'd be happy to lend you my shotgun.