ugh
5-string basses are not only for "shitty metal bands"
Lots of amazing musicians in other forms of music use 5-string basses (and even 6-string basses.)
Marcus Miller plays 4 and 5 string basses, and he is probably one of the best bass players in modern music.
To put it simply, you have more range in tone with them.
Personally, I don't like them, but that's not to say someone is stupid for wanting to get one.