The main reason I choose to waste (spend) my time answering questions is I want to help someone who legitimately needs help. I'm positive that a good number of monks here feel the same way. If I stop believing that, I have little incentive to answer someone's question. That would hurt the community.

If you read some of the plagiarized nodes (particularly where one answers the other) you can quite plainly see that they didn't understand the question or the answer they pasted (generally way off topic). Learning was not the purpose of their post. It's a waste of our time.

As for outsiders who search - Then they should presumably be able to find the original content. Lets say a perl beginner finds a PM node in question here, there's a good chance the earliest reply (remember AM's have replies sorted by post time) is reply from the one of the participants. Which means there's a good chance that the first reply is a completely off-topic and wrong.