There's an argument I've seen - no idea whether it's correct - that users acclimatise to new advertising technology and eventually regress back to the mean. I suppose this would mean that newer and more invasive ads cause a spike in consumer spending, which drops over time until the next innovation.
I've never seen someone make that argument for better targeting, which is what they're saying cookies enable. You're not going to acclimate to being more interested in the ads you're seeing.
The argument for better targeting is simple: targeting works (whether directly or just through being a novelty), and those who engage in it get ahead of those who don't.
The argument for getting used to ads is mostly psychology/neuroscience.
