Yeah. If you buy a car stereo with minor crowbar damage from some guy selling out of his trunk, you could make the same argument.

As for the gate telling the F/A to seat the pax in F, the F/A is going to want in on the action too, or will just report the agent. If you're going to bribe the F/A, you might as well do it directly.

As for why they don't fill up 1st, this has been long argued around here. The con argument is that if they make it too easy to get into F for cheap or free, people won't pay for F and will just take their chances on getting upgraded.