It's more like blocking exploits, I'd say. Which your prototypically clueless Grandma is vulnerable to. So her machine is likely sending spam, or worse.
Let's not confuse invasive ads and tracking cookies with "exploits." We can dislike both, but they are definitively not the same thing and one is clearly a bigger real threat than the other.
I consider tracking to be an exploit.
I mean, there are laws against stalking, right?
how many times do ad services have to inadvertently push malware until we can just lump them into the 'malicious' category?