I don't think anything is particularly arbitrary or contradictory about that idea.
https://en.wikipedia.org/wiki/Continuum_fallacy
Just because there is no sharp division between two states, doesn't mean they don't exist to begin with.
Quantity has a quality all its own
Your friend starts a company, you become friends with his employees. Eventually you start a company a really want to offer an amazing opportunity to one of your new friends but you don't because why?
Why are you denying someone the choice? It seems almost immoral that you wouldn't give her the choice and instead deny her the opportunity just because she happens to be employees by another friend
What if you had no faith that your friend's company would survive? Does that change your mind? What if you thought your friend's company would survive but never be more than limping along whereas you had faith that your company would become huge?
I ran a company,this issue came up when a friend asked if it was ok to poach from us. My first reaction was to think "no way" but my partners pointed out denying our employees opportunities was wrong. Fortunately none of them left.
Grow the fuck up or do not run a company. Childish viewpoints are for the playground. If your friend can't deal with the fact that you offer a more attractive work environment, he or she deserves for their company to tank and the smart employees will follow the first one who leaves.
It's "evil" in the sense that you are deliberately and dishonestly screwing employees in the worst possible way. It's exploitation.
The very reason this is illegal is because it's quite obviously morally and ethically wrong, but people are motivated to do it anyway.
The only difference is that on a small scale, you might not be caught, or you might be able to bluster your way out of the consequences.
But you can't really hold it against companies that are poaching. Whether or not they are friends with you because everyone in tech basically knows each other (through networks).
There seems to be a limited talent pool in specific skill sets for certain geographies. In this case, the market is in the favor of the employee, not necessarily the employer.
Remember, the law is often here to try to destroy "from now on" customs that are deemed toxic.