Corporations are afforded civil protections in return for civil responsibilities imposed on them by law. These responsibilities include restrictions on types of investment. Nobody's stopping an individual from starting a business, investing via entering a partnership, or investing by making some personal guarantee with another individuals. Corporations aren't people. When you make a deal with a corporation, you're actually making a deal with society, at least in part, so your deal will be upheld on paper. In order to reduce the risk of malfeasance and cost to itself in the form the consumption of legal resources, society imposes restrictions on corporations that include types of investment.
You can make the case that the regulations may or may not be the best for what society wants, but to say that they're somehow a moral obscenity seems silly to me.
I think it's strange to say that you're prevented from investing in a corporate structure because of legal limitations when the same legal limitations are what enable you to invest in the corporate structure in the first place. It's why I don't subscribe to this viewpoint on investing.
I agree with you on the gambling bit, to an extent. Government-backed lottery really preys on a certain class of people and I don't care for it so much. Private casino-style gambling is viewed by many as an entertainment outlet. Like drinking, for example. It's generally understood that you go to the casino to have a good time....and lose your money. Winning is understood to be an aberration. That doesn't stop people from blowing everything, though.