Let's say you are going about your business and interacting with a site...
Let's say it was a layer, instead of a modal. There is still, more often than not, a mechanism that tracks whether you interact with that layer. In protest, say you don't click to dismiss the layer at all. Is that ever recorded? therein lies the problem.
By no means am I an opponent of collecting metrics. I do think it is a very important process of the software development paradigm, but there is a right way and a wrong way. Too often are we bombarded with the wrong way.
Please read this useless message!!!
This content may or may not matter, but regardless - I've taken your experience away from the site by forcing you to consume this content without your consent.
What's more, I will record what you click on this dialog.
For the sake of making UX better...
Will I take this data and make my site better?
Meh, maybe. Maybe not. Who are you to me, user?
Either way... I've sacrificed UX for UX. It's a paradox and should be avoided.