Your vocal cords reach maturation somewhere between 24 years old and 30 years old. Asking a mature adult to sing like a 14 year old is the equivalent of asking them to look like a 12 year old at 40. It is just wrong. Some people do it, but only because they haven't had any vocal training and do not know any better. There are places where singing without vibrato is good.
Choral singing is such a place.
But, the straight tone must be produced freely, and not be forced. I hope that some of this has shed some insight into singing and vibrato. Someone from the Lake HS Band Student Body Vibrato does not harm voice at all. Vibrato is caused when the muscles that stabilize the larynx are relaxed, permitting the voice box to move a little. Stopping this natural process uses and strains muscles.