Follow Up on the Penalty Question

Yesterday afternoon's atrociously officiated game (more on that in a second) raised the question on the offsetting penalties question in the previous post.

With a little more than 6 minutes to go in the third quarter, Auburn up 20-17. Georgia returns the ball to the 32. Knowshon Moreno ran left into the line and lost three yards. Second and 13 from the 29. On a busted play, Stafford rolled right, scrambled for a while, then heaved the ball forward while stepping out of bounds on the Auburn sideline. Because of the scrambling, one of the linemen had gotten downfield, eliciting an ineligible man downfield penalty. This is a 5 yard penalty (if accepted). On the same play, Stafford was tackled out of bounds, drawing a personal foul penalty on Auburn. This is a 15 yard, automatic first down penalty.

By rule, the 5 yard penalty and the 15 yard/automatic first down penalties offset.

My questions:

1) Why do penalties for inequal infractions offset ever? By football's own rules, the personal foul penalty is a significantly more serious infraction - the punishment is far more severe. One penalty serves the purpose of punishing for a slight competitive advantage. The other serves the purpose of protecting players from injury. Why would two penalties that by no means are equal "cancel each other out"? Should not they mark off 5 yards one way, then 15 the other?

2) Does not the fact that these sort of penalties currently do "cancel each other out" give an unreasonable incentive to perform illegal actions? Say a defensive team sees a flag in an area where a penalty on the offense would be thrown (and that's not too hard to tell - holding penalties are in the backfield, illegal motion are from the side judge, and even on a scramble like in the play described above, the area where the penalty was thrown usually meant a penalty for holding, block in the back, clipping, or illegal man downfield (all against the offense). When a defender sees that flag fly, is it beyond the realm of possibility for the following thought process to start:

a) See flag, know that offense is likely moving back 5-10 yards and the result of the play is nullified.

b) If a particular player is particularly hard to defend or is running all over the place, might it not be of a greater advantage to forget about the 5-10 yards (and a repeat of the down - a mitigation of the penalty to the offense), and instead tackle/spear/trip/lunge at after the play that one player who is causing the defense so much trouble?

If the result of such illegal activity is simply that the 5-10 yards the offense would move back is no longer there, might the chance that the difficult-to-defend player could be taken out be worth it?

I'm not saying the Auburn hit on Stafford in the above-described play was intentional. I have no idea of knowing if that were the case, and I don't believe it was intentional. But hypothetically, a team very well could coach the players into going more aggressively after a foul on the offense has been thrown. Sort of the reverse of the offense getting a "free play" and going deep when they see a flag that looks like offsides on the defense. If the defense goes more aggressive and doesn't get called for anything, they haven't lost anything. If the defense goes more aggressive and does get called for a roughing or personal foul or something like that, they're in the exact same spot they were before the play started, except they have a chance at causing an injury to a particularly strong opponent.