The OEM safety system is just that, a system.
In a street car the lack of a rollcage, collapseable seats, retractable 3 pt harness, and the airbag all work together to provide optimal and practical safety.
In a racecar the rollcage, rigid seats, 5 or 6 point non-retractable harnesses, no airbag, and a helmet all work together to provide maximum safety.
Once you replace components from either system, without having the whole system, the safety equipment can become more of a hazard than a safety measure.