In this form, it's easy to show the flaw in this line of thought, because it concludes with literal extermination of the species ("the last person" implies no further people). And if a right leads to extermination of the species, what good was that right in the first place?
All rights have a balance point. Most hinge on where the rights of others begin. The freedom of speech (in the form of criticism of power) has massive value to the formation and maintenance of a free society, which is why some nations protect it so zealously. But even those nations have recognized its constraint in various contexts.
The position described here is a fringe position and should remain one to maximize the value of free speech.
?
Well, that depends on the amount of dying and the kind of speech.
Of course, if everyone died and the last person was able to speak freely, it would be worth it.
Everything else is trading safety for liberty.
Slippery slopes of free speech crackdowns inevitably lead to loss of liberty.
Leave if you don't like it.
Absolutism in free speech is the only justifiable position.
Welcome to debate.