Cars already have airbags and seatbelts which help a lot for the kind of collisions that would otherwise result in head injuries.
> It might make you much safer in case of a crash, according to your reasoning.
I don't see what in their comment could be construed to say that helmets make you much safer regardless of vehicle.
> Wearing a helmet can itself become a leading factor to cause an incident
Is there a source for this? Should be a randomized A/B test as you mentioned, not just a correlation - wearing a hi-vis jacket or other precautions taken more often in dangerous situations probably also correlate with accidents.
Even if helmets do cause accidents through increased carelessness, some may still take issue to intentionally making a scenario more dangerous such that people are more careful. It's kind of settling for a local minimum, rather than aiming to reduce inherent risk alongside aligning people's risk estimates to not overestimate the precautions.