As a safety conscious rider, it's hard to see this one way.
On one hand, the Sikh riders seem to really enjoy riding, and riding together. Nothing quite says "bad ass immigrant" like a flock of brown brothers on Harleys in matching turbans, rolling in a holiday parade. Turban and beard are very integral to their religious identity, no doubt about that.
On the other hand, riding without a helmet is a terrible idea, for both the rider and the community, which inevitably bears part of the consequences. Even purpose-built helmets without chin bars and face shields do little to change outcomes in the majority of crashes. Even at sub-freeway speeds. There are good reasons modern ECE and Snell ratings really require full-face helmets for street motorcycling applications.
I really, really hope this isn't a Sikh-specific rehash of the "party hat" phenomenon in the USA. Down here, some riders, and especially "scene" Harley-Davidson riders, reacted to helmet laws by selling cheap, minimal "helmets" that either claim to pass or just pass our laughably outdated DOT safety standards. These are little better than paper party hats, ticking a box to avoid obvious problems with police.
I'm not familiar with the full context in Canada. But law aside, anybody riding a motorcycle on public roads in a turban needs extra helpings of initial and refresher training, more insurance, and proactive estate planning.