If hat these people do fall under fair use i.e. make changes to the song or only use pieces of the song or some other thing of that nature then they should be allowed to use the song. However, if they just play most of the song without doing anything with it then they shouldn't be allowed to do that.
Bands should allow their songs to be used by individuals for personal use. It is a way to promote their music and expand the fan base by allowing more individuals to use their songs. It may seem like the creative control is relinquished but the rewards of sharing the music are also financial as well as promotional.
Bands should allow more individuals to use their songs for personal use, because doing so will further promote the popularity of their songs. People are more likely to buy a band's music if they hear several songs they like from the band. Allowing people to use a band's music for personal use gives a band much more exposure.
Bands should not allow more people to use there songs because it is personal. Artists create things that show a part of them. They fact that they choose to share their talents if a gift in itself. Sometimes , allow others to perform their art in public can be simply to intimate a commitment and that is ok.