I feel people are especially against it because it's largely wealthy westerners (even redneck hillbillies are wealth vs like amazon tribes yano?) who participate in it as a sport/tradition. Fox hunting has been a big deal here in the UK, large groups of people ride on horses with packs of dogs bred to hunt and destroy (literally... DESTROY) wild foxes for sport.
If it was a tradition of less priviledged, older civilisations it would be less frowned upon. If for example the Masai tribes in Kenya/Tanzania hunted for sport rather than food etc. it wouldn't be such a big deal.
An argument against hunting that I hear often is (regarding trophy hunting anyway like the Impala etc) suff about endangered species etc. I'm pretty sure that the only way to trophy hunt is to pay an ass load of money to hunt specifically bred animals on a reserve. In some cases captive breeding for the purposes of trophy hunting are actually helping to support populations of species which are fairly low in number. You could argue about the validity of supporting a population by breeding in captivity but it's not entirely different to a zoo. Sure in a zoo the point of breeding an animal isnt to kill it, but it is to raise it in captivity. Usually the encolsure size of animals in a zoo is actually smaller than most hunting parks. Animals raised to be killed for sport arguably have a greater quality of life. When it comes to killing the animal, the point is usually as quick, clean and efficient a kill as possible. With a good shot the animal is dead before it hits the ground, when they are left wounded and escape they are tracked down and quickly killed as humanely as possible. The quality of life/stress of being hunted/injured for raised animals are actually fairly difficult to asail.
In my opinion it only really comes down to people views on the morality of killing an animal for no reason other than your own satisfaction. In response to that I'd argue that if one of your greatest concerns/moral pet hates is hunting then you're not paying enough attention to world news. Further to that, this argument about morality simply boils down to opinon and upbringing. Any argument about what is right or wrong is doomed to remain for ever unresolved as there is no universal guidlines as to what is right or wrong. We have governing laws, by which in most places hunting of some sort is legal, so if your argument is it's morally wrong then governments actually seem to disagree with you, not just the hunters.