Its better to play a bad song then to piss off an asset to the band. If one person likes the song surely someone else does. Mabey you think its a bad idea because its not your style; or mabey the arrangment isn't the best for lyrics. I would write the lyrics for each section, record the song and then collaborate with the writter of the music and the band on how to arrange the song for the best structure for the lyrics all parts considered. As long as you don't discredit his ideas he will probabily stay open to yours. If music were looked at in percentages, 50% of the song is the music and 50% of the song is Lyrical. Anyways, after you get that sorted out get a new recording of the song and show it to as many people as you can, and see what they think. I think record companies expect you to sell 100,000 units or something like that nation wide. So if you find one other person other then the writter who likes it, then there you go.