So basically, it doesn't make sense to place shares with "friendly", existing shareholders.

As long as you issue warrants, participants will short the hell out of the stock to go for immediate profit, whether they are known or unknown shareholders. You might even argue that existing shareholders are the worse choice, since they already own a lot of shares and have an incentive to even sell off their existing holdings in exchange for the warrants.

Who the heck (in the financial industry) invented that little extra "sweety" called a purchase warrant. Shouldn't it be enough of an incentive to 1) pay below the existing share price and 2) be able to buy a large quantity of shares without moving the share price?

The addition of warrants is an example of a perverse incentive, because it leads to instantaneous profit and has a significant cost for company and existing shareholders.