The most common argument against it is that if fighters know they are winning going in to the final round(s), then they're more likely to coast and you could end up with boring fights.
However, of course, the inverse is true, in that the fighter who knows he's losing will (should) go balls to the wall, looking for a finish.
Personally, I'm for it. I think it could really amp up the atmosphere in the arena, under several circumstances.
+ Fighter realises he's down, has to go for it and the crowd will be either behind him/against him.
+ Can you imagine the crowd reaction to a bullshit call by the judges? The place would go nuts and it would fire up the slighted fighter too, making him do more to secure the next round.
+ It would clear up any confusion as to who is winning the fight, because, as I'm sure we've all seen, it's pretty common to see both corners tell their fighter that they won the previous round.
- One negative is that it would sometimes remove the anticipation of the reading of the judges decision as, more often than not, we'd already know who'd won the fight. Although I suppose they could not reveal the final rounds scoring until the judges decision is read.