On my first serious job in 1990 I was the only developer working in my department and didn't know to use source control.

Pretty soon thereafter I learned, from then on I've never seen a project that didn't make it one of the first things they set up.

I nearly lost all my work at that job because I deleted a folder at the wrong level. Luckily I had brought a copy home on a 5" floppy the week before and was able to re-create the weeks work in a few long days.

So I guess I'd consider it acceptable if it was the first project for everyone on the team and nobody knew better, but if even one person could actually explain the benefits and the team still didn't listen I'd re-categorize my opinion of the group from "naive" to "dangerously incompetent" (Resistance to using a tool with such widely-demonstrated benefits is almost criminal--it's like if your team didn't trust "Compilers" and insisted in doing everything in assembly language).