If doing that is really practical, I would tend to wonder if the employer has a practical business plan. Shouldn't your employer be adding enough value to your code and work processes that you couldn't make the same product without them?
At the job I currently work, our product is for a very specialized domain. I can remember the problems that I've solved, but there's no way I could build or sell a product in the same market without the domain expertise that my employer brings to the table.
Maybe your employer is providing capital to fund the salaries of a team of developers to build a product that has no guarantee of any market success, saving you the trouble of risking that kind of money, or convincing somebody else to risk it for you.
Maybe you don't like sales, and your employer is going out to potential customers and convincing them to use your product, so you can keep working on the stuff you're really good at.
Point is, if you legitimately can't think of some value that your employer adds to your work, maybe you really should take off and do the same thing for yourself.
That was more of a hypothetical scenario than my actual life -- I'm a researcher working in academia, so in my case, I pretty much do do all the work around what I produce (my university provides support in terms of office space, administrative staff, etc., of course, but the "product" is research papers that they don't have much of a hand in).
But that aside, I'm not sure you got my point. Something doesn't have to be easy to do in order for it to be illegal. There are lots of reasons why a person might not want to do this -- you mention several of them. But that also doesn't mean that the employer shouldn't have the right to prevent them from doing it if they did want to. If your employer is paying for you to figure out how to solve a particular problem, generally the employer gets ownership of that work. If you then duplicate it on your own, it's a pretty gray area as to whether the employer gets some claim over it.
At the job I currently work, our product is for a very specialized domain. I can remember the problems that I've solved, but there's no way I could build or sell a product in the same market without the domain expertise that my employer brings to the table.
Maybe your employer is providing capital to fund the salaries of a team of developers to build a product that has no guarantee of any market success, saving you the trouble of risking that kind of money, or convincing somebody else to risk it for you.
Maybe you don't like sales, and your employer is going out to potential customers and convincing them to use your product, so you can keep working on the stuff you're really good at.
Point is, if you legitimately can't think of some value that your employer adds to your work, maybe you really should take off and do the same thing for yourself.