Please tell me where the app has "it's uses" here?
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.