This is not different from using drugs to win sports which hasn't yet been banned because it is too new. Strictly speaking it is legal, but it is both immoral and unethical.
The problem with depending on every possible behavior being described in the law and closing every loophole is that that would create a very draconian legal system nobody wants.
It is the same as with contracts between two parties. It is easy to screw each other over if one nitpicks about everything and don't follow the spirit of the contract. However the problem with such behavior is that it dramatically increases transaction costs, because one can not trust each other and have to make extremely complicated legal contracts.
I've noticed when dealing with American how the lack of any trust, makes any kind of business deal very expensive. Contracts are completely over the top.
I don't think this is how one wants society to develop. Parties in an economy have to be able to play fair with each other most of the time without resorting to ever more insane details and regulations.
Should I feel bad?
More specifically, does this violate the "spirit of the law?"
Even more specifically, every other rental owner does the same thing, so even if I change my behavior, I'm at a disadvantage with my competitors.
Again, your issues are with the government, not the companies that are following the law.
BTW why do you bother as a shareholder, do you receive any dividends?
There are probably a lot of reasons that people invest in corporations that don't pay a dividend. The "most obvious" is that you believe the company is growing. The organization will reinvest in itself -- instead of paying you a dividend -- and increase share price to a degree greater than you would have gotten with a quarterly dividend.