Interesting point on children's perspective. They're lacking the habit of reading documentation that comes with anything and the proper knowledge about sponsor ware.
Actually, more intermediate or even advanced users could make similar mistakes, but for different causes.
I accidentally installed them the first time I used MsgPlus. I'm sure like a lot, I'm used to installing many programs so clicking "next" in a hurry during the process seems pretty natural to me. When I was greeted by the sponsor ware screen, my first reaction was that it was just a typical user's license agreement (quick decision given that I deemed there was nothing atypical about msgPlus), but...you know the story.
I'm not complaining, though, as users should be grateful for a good program and its programmers should be rewarded. Therefore I'm planning to get some MsgPlus! wares so next time it'll be more convincingly and comfortably for me to refuse installing those sponsor ware.