The primary function of free speech in a society is to root out bad ideas through criticism, which will in time leave its people with an ever deepening pool of good ideas that are hard to vary. In other words, ideas can eventually become so strong that they are difficult to change, or “vary”, without also making them less good in some way. The more ideas a society has that are hard to vary, the better off its citizens will be.
Thus, speech advocates defend offensive speech not because we enjoy “punching down” at the weak, but because we know that eliminating such ideas through threat or force is a mathematical problem that also reduces the number of good ideas in a society. This is also known as “chilling speech” — because it increases the risk of speaking some good ideas so much that many people will stop speaking them. Instead, we advocate for countering offensive speech with stronger ideas, rather than trying to eliminate them altogether.
Unfortunately, the creeping desire by the left, and in some cases the right, to consider more and more variations of speech “hate speech” risks our ability to maintain the largest possible pool of good ideas, which is why we should be careful about the use of that term. Obviously, there are some forms of speech that are reasonably off limits (such as yelling fire in a crowded theater, calling for mass genocide over public airwaves, etc), so there is justification for placing some constraints on very specific kinds of speech — even if that means some good ideas might also be lost. But when deciding which speech is off limits, we should do so with a scalpel and not a hammer, because better outcomes for the future of humanity is, ultimately, what’s most at stake.