Automatic failure for not completing all assignments - proper?
your question needs a step back: is university the place to force students' personal behavior and personal decisions?  if yes, then what is the difference between university and school? 

My view is simple: University is the transitional place where students learn to make their own decisions and be responsible in preparation for real-life. This means that there is no one anymore chasing you to "please study". At university you are responsible for your own learning and students quickly start learning responsibility after a little while. 

If we are going to keep holding the metaphorical stick and say "you HAVE to do everything as i told you to or else" then when will these students learn to make decisions or realize the  consequences of bad decisions in a relatively safe Environment?   

Then comes the 2nd question: Is it for you as a university educator to actually force students to do assignments? why? 

If they want to have better learning experience from your class they will choose to do more work. If not then not. It is really not your business, their grades cover their learning. whether or not they choose if your class is worth remembering after the  semester end is their own choice. 

Finally, some university professors make me feel they just want to control students. I had various discussions before about why for example you'd be offended of having your student use a laptop in lecture or look at his/her phone (this seems to be more common in the USA instructors than in other countries I dealt with for some reason). 

Of course I expect like a million comment now about how you are supposed to "do what is best for them". Except that that they are no longer children, what is good for them is to teach them to be adults. This means: guide them not force them