The fallacy in your argument is that your enterprise consists solely of your property. If machinery and buildings and equipment could do everything you need done, you wouldn’t be hiring workers. So your employees become an integral part of your company’s success.
They also acquire a vested interest in its effective management, since their livelihoods (and by extension, the welfare of their families) depend on the company remaining viable. Not to mention that they risk their health, their limbs, even their lives to earn a paycheck for themselves and drive a profit for you.
The real tragedies of unions is that they create an artificially adversarial relationship between labor and managements (where in truth that relationship is symbiotic), and that they were ever necessary in the first place.
Only I can decide what is an integral part of my company, and I should be able to fire a union guy at any time I choose. Unions don’t create the adversarial relationship — welfare begging bums who think they are entitled to the property of others create it. Unions just empower it.