For me it's not so much seeing ads as the tracking, the performance load, and the battery load that the ads bring.
Let's not forget about being forced to spend some amount of your data plan for the "privilege" of downloading and viewing the ads... and that several of those ads will install malware, nagware, scareware, etc., if you miss the "close/dismiss" button. Of course, when you complain to the websites about it, they will say that they get all of their ads from RandomAdNetwork... and if you ask RandomAdNetwork, they'll tell you that they're just a distributor and aren't responsible. So basically, until someone tells me where I can point the finger of blame when these ads do nasty stuff to my phone, tablet, or computer, I will use whatever ad blockers I please, and if I can't read whatever site it is because they won't allow ad blocker usage, well, I guess I'll go elsewhere.