Spoiler:
I agree, the cloning device is a little far fetched (okay, impossible, anybody who knows anything about physics should know that you don't create something out of nothing. It would've been more believable if it really just teleported him) but it really isn't about the believability of the device and more about how Angers uses the device. Borden is completely dedicated to his art and maybe playing his wife and mistress like he did was wrong but not quite on the level of wrong that Angers is at when he is killing all his clones.

Spoiler:
Judging from Cutter's description of drowning I'd say that Angers choice was deplorable. Basically, it's about the ethics of cloning and whether or not that clone is a part of you to which you may dispose of it as you wish or whether that clone is a completely different person. The way I see it, the two Angers are the exact same person until they split. So when they split their entire past conciousness is copied to each one. The one who reappears at the top of the amphitheatre is under the impression that he has teleported while the one who falls into the water feels as if he has just fallen. Now when he goes to do the trick again, the one who was copied onto the upper balcony is now going to die while a new copy will be made to appear up above. In essence, Angers is first handly killing his clones where the death of Borden's wife was unintentional. Maybe Borden could have seen it coming but he wasn't premeditatively killing whereas Angers was.

Spoiler:
The way I see it is that each clone dies when it tries to perform the trick. Basically, the first person to die was Angers, then when the trick was done again it was his first clone that died as the second clone was created up on the balcony. The thing is that the conciousness of this clone was identical to the one that dies up until the copy occurs. So the Angers that is alive at the end feels as if he's been safe everytime though he still has the fear that he won't be.