There are a slew of reasons that people post replies that are incorrect in some part. Most often it is an oversight and almost always the problem is picked up and discussed by others.

Imploring people to only provide "correct" answers not only doesn't fix the problem, it actually lowers the quality and value of PerlMonks! One very important aspect of the PerlMonks community is that discussion of questions takes place on many levels and therefore matches well to the many levels of understanding of the various monks. A simplistic answer may miss subtle but important issues, and therefore be "wrong", but will very likely provide a stepping stone to greater understanding by the author of the "wrong" node as well as greater understanding by other monks at a similar level in their journey to mastering Perl and its environs. Wrong answers are often much more valuable for this reason than a simple reply giving some correct code without exposition.

Reputation is important here. It encourages people to post and helps maintain high quality posts. The XP system expands in node reputation by providing a sort of global reputation based on participation and quality of participation. The system is somewhat open to abuse, but generally works very well. A major reason that the monastery is such a welcoming and helpful place is that the XP system encourages that atmosphere and encourages participation.

Remember too that a node's reputation is not available until after you vote for the node except through best nodes. By the time a reply accrues enough ++ votes to hit best nodes it has been seen by a good number of people and it is pretty unlikely that a significant error will go unnoticed.

The system currently works well. Wrong answers seldom go unanswered. Leave well enough alone I say.