The issue isn't security. The issue is control. The Debian project uses signed packages to ensure integrity but is open regardless. Of course there should be security and a reasonable expectation of utility but not at the cost of free use of something you bought and own. The tech industry is moving to a concept that you "rent", for lack of a better term, rather than own something you purchase. I have no issue with commercial software but all software is useless without the hardware to run it. If I have the hardware, I should be able to do what I want with it, just like an automobile. What's the difference? If a car manufacturer decided which highways you could drive on, based on a restrictive license agreement, you wouldn't buy that car, but you wouldn't buy a car without seatbelts. We wouldn't accept this concept in any other situation, why do we accept it in this situation?
Apple dictates the apps can you use and restricts the OS. It's not a matter of signed packages and security, but of corporate domination of technology and restriction of use of a hardware device you legitimately own. Would you buy a PC that restricts what OS and software you can run on it? But when it comes to smart phone and tablets, we except this. Blocking nefarious apps is one thing, having absolute control of what your computer and or smartphone can run (yes smartphones are just portable computers)is a monopoly. We wouldn't except this in any other industry. If Ford decided that you cant modify, improve or repair their products based on a restrictive license you had to agree to on purchase, you probably wouldn't buy a car from them. In the tech or media industries this is acceptable. Why should we accept a "walled garden" on smart phones when we own the hardware? If it were any other industry, people would be outraged.