If I could, I'd like to throw something new out there: I believe megan3221 referred to this as "garbage" not only because she didn't agree with the message it was sending, but because the song has absolutely no substance at all. Its a stupid pop song. No one can honestly say any different. Like most pop songs, its only good for three things: dancing to it, making fun of it, and generating money for the artist.
DISCLAIMER: I saw this comment on a Britney fansite, and I thought it was a pretty good opinion.
Credit goes to the girl who wrote it (Kelly) for having an open mind.
"I posted this on the chat box earlier, but incase anyone feels a little uncomfortable with the song, try thinking of it like this: "Peter, Paul, and Mary" can be taken in two contexts - The biblical one, and the "common names" one.
We'll go with the religious relation, then. (The actual writer(s) of the song probably wrote it in for shock effect, though.)
Anyway, since "Peter, Paul, and Mary" were said to be followers of Jesus, the song might be a subtle reference that compares Britney to Jesus. (LOL, no, Britney is not a deity! XD)
I'm talking about Britney's influence over millions of people. The three people in question might be a reference to fans in general (here's where the "common names" context comes in, since anybody can be her fan), where their loyalty to someone they idolize makes them open or easily persuaded to try something because of how significant they think their idol is.
In that way, it can be said that because she's suggesting a threesome, her fans (or whoever) might agree to it, because Britney asks/tells them to.
For the lazy: Maybe it's Britney's influence over her fans being compared (quite dramatically) to Jesus' influence over these three particular people in that one line."
As "Wajiha23" pointed out, there is so much worse than this on the radio. Kids listen to it, yes, but kids always engage in things not intended for them. They get ahold of cigarettes, drugs, alcohol, pornography, etc. Its a part of life. Not everything is intended to be child friendly. Look at the shows on t.v. now-a-days, especially animated shows like Family Guy and South Park.
Britney Spears sings pop music. It is short for "Popular Music," which means it is designed to sell millions of copies. "3" is another example of a probably successful single.