Carl, his floating house and a Boy Scout named Russell somehow make it to South America and inadvertently befriend the same strange-looking bird Charles Muntz has been looking for all these years. As a result, Muntz sets Carl's house on fire, kidnaps Russell and then tries to kill them both by sending an army of talking dogs to shoot them in little planes.
There's a pun somewhere in here.
The Pointless Evil:
And don't say, "Because he was evil!" Even in terms of carrying out an evil plan to kidnap a rare bird, it doesn't make sense.
Things turn ugly at first because Muntz thinks Carl and Russell have come to steal the bird and rob him of his discovery, but Carl's story should have been verified once Muntz realized that he really did travel to South America in a floating house (if he was telling the truth about that, we'd believe literally anything else he said).
It's because he's old. Once you lose the ability to poop, everyone must pay.