If someone disconnects, when they reconnect they will still be in the dungeon and party with you. As for adding someone after getting kicked....sure, why not be able to kick all your party mates and invite your friends instead? No potential for abuse there, not at all.
I agree it's not fair, but unfortunately I don't think it should be changed. It will probably only be an issue for a little while, because of the initial open beta launch. Once the queue situation dies down, it will be working as intended.
There are no "free" players in this game, because the game itself is "free" to play. At some point almost everyone will probably spend a few dollars on something, and then what's the difference between them and you? Do you think you're better than everyone else because you spent a lot of money at once, before the game…
If there is such a passive, it should show up somewhere further down your powers list. You can access this by pressing the C key, then click the powers tab. Take a look and see what you find.