It correlates well with the useful work for the sites.
That is the intent with reputation, yes. But this does not mean that there are not parasitic means of attaining rep, ways which garner reputation without meaningfully generating useful work.
For example, money often correlates with doing useful work for society. But it would be difficult to argue that Bernie Madoff genuinely contributed useful work to society, yet he managed to attain quite a bit of money.
The problem is not people who "want reputation". The problem is people who want reputation without giving any thought to whether the things they're doing to get it are genuinely useful.
At the end of the day, what we want is useful work. If you try to do what you do just to attain reputation, then you are incentivized to find a way to attain rep while doing minimal work. Even more to the point, if you only care about getting more rep, then rules which exist to ensure that contributions achieve some standard of quality are things which get in your way. In such a world-view, the only quality that exists is voting.
And then you've reached that parasitic point. Such a user does not care about actual quality, merely about whatever you can convince others is worthy of an upvote. To such a user, a closed question is not preventing poor quality posts; it is preventing them from getting rep. To such a user, a downvoted question is not a statement of the question's quality; it forces the question off of the front page and thus reduces their ability to gain rep from answering it. Downvoting and close voting are not tools of quality control; they are mechanisms that limit that user's ability to generate reputation.
A user who looks on questions as a potential reputation generation engine is using a mental model of the site that is not based on producing good content. It's based on getting a bigger number. And since we want a site that produces good content rather than bigger numbers, we must therefore be antagonistic towards a view of reputation as a goal.
My personal experience is that people with high rep, but mostly crap posts, are rare (well recently I've seen some semi-literate user on the SO with 8k). My another personal experience is that there is f*g hard to get a lot of rep, and people should be encouraged to work on it and not deterred from it.
Here, we see an interesting take on rep farming. It would seem that your perspective on the subject here is focused on how successful the activity is rather than the activity itself. That is, if someone is a rep farmer, then they must have a lot of rep. And if they don't have a lot of rep, then they're not a rep farmer.
Rep farming in this view is defined not by what you're doing, but by being successful at it.
That makes no sense. Even the word "farming" itself is defined by a process, an action performed, not the results of that action. Even though the very definition of the word "farming" is to produce food, farmers can in fact starve. They can go through the motions, yet not produce sufficient amounts of the food they desire.
There's that old saying: it's called "fishing", not "catching".
Rep farming is defined by the process, not by the results. People are rep farmers because they're doing things to increase their rep which are not helpful to the purpose of the site. They make a lot of posts, not because they're good at sharing information or have good information to share but because casting a wide net is a good rep farming strategy. They try to post first regardless of quality, because posting first matters more for scoring rep early on than quality. They use their voting to keep questions "alive" even if they shouldn't be. Etc.
The reason why rep farming is bad is because it encourages bad behavior. It doesn't matter if those bad behaviors are not actually a good way to get rep long-term; the view of reputation as a goal still encourages their behavior.
And that's another point in the Madoff analogy: Ponzi schemes often don't work. They certainly don't often work to Madoff levels. But the fact that a person can make that much money off of them is not why we forbid them. It's not about how much you might make; it's about what you are doing to make it.
Without the motivation of the rep, the SO would be now a coderanch.
I cannot deny the utility of reputation as a motivator (particular when it gives you powers on the site). However, once you reach a certain threshold, reputation stops being a useful motivator because, well, you have enough. So if what you were saying is true... why am I still here?
I'm not here because I really want to get to three hundred and four thousand reputation. I'm here because this place is not a forum. I'm here because I can spend my time on decent questions since garbage, time-wasting questions have a quick and brutal end. I'm here because good questions appear which warrant my expertise. I'm here because this place catalogs good content in a way that's easy to find. And I'm here because, due to all of those things, the answers I contribute can be easily found for years later.
The feeling I get when I get an upvote on an old answer is not about getting 10 rep. It's about knowing that some answer I wrote off the cuff half a decade ago managed to help someone.
A view of reputation that sees it as gratitude given for having provided good content is a view of reputation as a measurement of the quality of content. Viewing reputation as a goal is, from that perspective, perverse. It's as ethically perverse as saying you should help people to hear them say "thank you".
This was a comment on another answer, but I think dealing with it speaks to the fundamental issue at play here:
No, I am encouraging people to collect so many rep as they can. Questions are nearly unusable to collect rep. Everybody knows, the only way to collect a lot of rep, is writing a lot of useful answers.
If your intent is to get people to write "a lot of useful answers", then telling them "to collect so many rep as they can" is... silly. Even if we work from the position that all of your assumptions are valid (rep == quality, answers are the only way to gain rep, etc), if your true goal is to encourage people to write "a lot of useful answers", why wouldn't you just tell them to do exactly that.
Because that's not your goal. The purpose of this post, as stated in another comment, is really something quite different. To you, this whole discussion is about dealing with this:
a toxic, suppressive atmosphere
That is what this is about. You want "rep farmer" to stop being a pejorative, not because it will increase the quality of answers on the site, but because it will deal with this "toxic, suppressive atmosphere".
It is this kind of thing that I find most interesting. That you're trying to hide your true goal behind something innocuous; your willingness to pretend to argue in favor of something seemingly innocuous while instead trying to accomplish something that would be more controversial.