Classical music is only inherently bad if the neshama of the composer was immoral. Otherwise it’s fine to listen to. Many of the songs by Jewish singers, however, have been copied, adapted from or completely ripped off non-Jewish pop songs, some of which are very low indeed. Unfortunately I do know the originals of some of these songs. Aside from having been copied from non-Jewish music, the act of copying the music itself is an aveira (stealing, since they have not asked the original singer’s permission) and does not show a good moral character on the part of these Jewish singers. Therefore, going by the same argument that some hold for classical music, this music would also be considered ‘not Jewish’.
Writersoul, you have really got me started on a pet peeve!