When you buy a physical object, such as a home, a car, a shirt, or a smartphone, shouldn't you be be able to repair it, modify it however you want, use it for different purposes, loan it to friends, sell it to others, and so on -- you know, all the rights and benefits associated with the concept of private ownership ? And when you buy a software object, shouldn't you have the same rights and benefits?
> shouldn't you be be able to ... modify it however you want
Not necessarily. Consider products that require radios like satellite internet transceivers. If you were allowed to "modify it however you want" you could easily modify it to put up a continuous wave and effectively DoS the satellite gateway, causing an outage for all other customers on the entire beam which is obviously something the ISP wants to avoid at all costs.
Hence, many companies only allow you to lease the transceiver, not own. And even if you did literally own it, they obviously don't want you modifying it for fear of harming the service of other customers.
It's one thing if you buy a toaster and modify your toaster to burn cool patterns into your toast. It's quite another if you buy a toaster and modify your toaster such that nobody else's toaster in the neighborhood works anymore.