Well, they're not wrong that the sports car will (likely) not be as safe as say a Model S. That said, it will have more advanced and newer safety features as well so you're not exactly comparing apples to apples since the Model S is effectively a decade-old-design. There may be an update to the S/X that makes this a moot point mind you. That said, in a vacuum, a sports car will be less safe than a compact sedan which will be less safe than a full-size sedan that will be less save than a full size SUV that will be less safe than a semi, etc.
You're right in that Tesla makes the safest cars on the planet and it's not even close. The difference in safety between the Tesla Models is minuscule especially when you compare it to that of other ICE vehicles. It's really not even worth splitting hairs over between the lineup when they're all heads and shoulders above the competition. It's likely that the new Tesla Roadster will be safer than most well-known "safe" ICE vehicle sedan offerings once the dust settles. You also have to factor in things like Autopilot, shorter braking distances and better handling that can all work together to keep you from even getting in an accident in the first place.
After all, when it comes to the physics of impact it's hard to absorb frontal impact with 3-4in. of crumple zone whereas a Tesla has 3-4ft. This is echoed in the beefier side impact beams and all of the other aspects of a Tesla that is engineered to either avoid an accident or make the effects of said accident less impactful for the occupants. This has been and always will be the focus for Tesla and it won't change on the Roadster.