What is your countermeasure to the dragon flying in, snatching a fighter, flying off, breathing on him (no reflex save to avoid damage) and dropping him far away and far below?
Although it's no picnic for the designated victim, it's not actually all that helpful to the dragon. The dragon gives up the benefits of obscuring mist by doing so, and gains, at best, lesser benefits from darkness, which is already not a game-changer in this scenario.
Per improved grab (which snatch is a special case of), it is certainly possible for the dragon for the dragon to move with the fighter. However, the dragon has a dilemma. It can grapple at -20, making the fighter grappled but not becoming grappled itself, allowing it to fly at full speed, but probably dropping the fighter in one round. Bite + breath weapon (no save) + 1d6 x 1d6 fall damage is actually not that impressive damage-wise for two rounds of actions. Alternatively, it can grapple, at its full bonus, which is 12 points in its favor, but means no Dex bonus to AC and half movement rate (to 75 feet), in addition to being able to make no further standard actions until it drops its cargo.
As a poor flyer, it can fly 75 feet per round, moving at an up angle of 45 degrees, giving it roughtly 30 feet of climb each round. At that rate, the dragon is going to have trouble getting away from the fighters. True, half the arrows will hit the designate victim instead of the dragon, but it's going to take a lot of damage. When it comes to the conclusion that the height it has achieved will finish off its now breathed upon, slightly feathered victim, it can drop him, whereupon it will begin to talk all of the damage from the arrows being fired at it on its return trip. It is fairly likely it can kill its chosen victim, but it would have to be very determined, as it would take a lot of damage and place itself at risk of being killed if it tried to repeat the performance. All that is assuming fairly open ground.
All of that assumes, of course, very unfavorable circumstances. If the fighter is a normal party, any number of simple countermeasures wille expose the dragon to fierce attack, and if the fighter is backed up by another party member with IPS, the curve will bend against the dragon significantly. It assumes also no such preparations as energy damage arrows or wands, as well; I don't think it's useful to assume great prescience when considering scenarios like this, but I think it's fair to acknowledge the fighter probably has at least some advantage not accounted for. The dragon, for its part, is a poor spellcaster.
Just as a technical point, Large black dragons are not eligible for Snatch, which requires Huge size. While it is possible that may have overstated the difficulty in this encounter, I am relatively sure there are other Huge creatures in that CR band that could perform similarly.