If you understand this, why do you chastise Intel for protecting its investment. The other key purpose of trademark law is to protect consumers from being ripped off.
Trademarks are an indicator of source.
If everyone were free to adopt symbols and names that are identical or confusingly similar to well known trademarks, consumers would have no way of knowing that they are getting the product they asked for. Similarly, when you order a computer with an MMX chip, you know exactly what you are getting and where it came from. That would not be the case if anybody could slap MMX on any chips that they please. I am not saying Intel's motives are entirely altruistic. Obviously, Intel is protecting its own interests.