I look at it this way....
If you fail to leave CAP above the field you choose to rearm at, or choose a field closer to the frontlines, you're putting yourself at risk.
Now the main reason you're doing so, is to gain an advantage over the enemy, in that you don't have to fly as far to rearm, and thus enter the fight that much quicker.
I see absolutely NO reason whatsoever to not attack aircraft on the ground if they've chosen to not take precautions to prevent such an attack. You're taking a risk, to gain something. If you are willing to take that risk, you need to accept the consequences.