Why, yes, free speech does help spread all ideas, including those which lead to death.

The only truly safe environment is a very strict prison where inmates are not allowed to do basically anything, because anything can be risky and ultimately lead to death. Ideally, thinking should also be restricted for the same reason.

Danger cannot be removed from trying new things and learning unknown things. Danger, suffering, and death are inseparable from any progress.

So it goes. Don't try to make an environment too safe, because it's inevitably stifling.