If we're referring to preforming outside of your home singing is a must. Haven't seen an act yet and I've seen alot that doesn't have vocals and thats whats fearured. Many mediocore,guitar players here but no one cares if the vocals are good. Even at the more pro level its all about singers.
As far as " I can't " yes you can it may just take more work than someone else. I sang all the way up thru college but never as a soloist. Found a great teacher who used to sing at the Met. She helped me "find my voice" and in time I was preforming out at gigs I,m not great, but have been told I have a good voice. I taught music in schools and worked with a lot of kids who said "I can't" So do it , find a teacher or youtube some lessons and take some time to work on it every day. It willl happen.