How is it going to screw your system? And just disallow running in background, disallow internet access if you are on mobile. I don't want to fiddle around with my browser when I can install a light-weight app.
Not everyone is a "wow all apps very scary" person
If I were installing a knot app and it required enrolling me in their Knot Tying Social Network, I'd uninstall. In fact, if it couldn't run in Airplane Mode, I'd uninstall it.