"is payola bad?"

Yes IT IS
according to laws
1-guy pay to make his song be played on radio after or before the song play the radio station say "this song was advertised by artist x"
2-guy pay to have his song played on radio. the station say nothing about this.

according to laws the situation 1 is not payola but situation 2 is.

THE REAL QUESTION BECOME:
WHY THE FUCK DO YOU SPECIFICALLY NOT WANT THAT THE LISTENERS KNOW YOU HAVE ADVERTISED YOUR SONG ON THE STATION?