The site norms about this have gradually changed over the years, so it may be helpful to take a bit of "historical" look at the problem. I think it sheds some additional light.
Also, I try to explain how the scale, more precisely, the growth of the site also plays a role.
StackOverflow is a couple of years older than us, and an order of magnitude bigger. So it may be a good idea to link to a few posts I find relevant. Both the posts I want to encourage you to read were written by Shog9 - one of the community managers working for StackExchange. He has extensive understanding of the dynamics of these sites (it's his job). He is also one of the CMs who regularly interacts with Math.SE moderators, and, when needed, will post here.
You are welcome to think that I am horribly misrepresenting his points. I probably am. You see, he is using metaphors necessarily open to interpretation. See for yourselves. His older post and a more recent one. I probably shouldn't try my hand using an agricultural metaphor, but I will do it anyway :-)
You can have a field day (bad pun intended) breaking my metaphor. It will do just that. Probably faster than I expect it to.
In its infancy this site did not have this problem. There was room for everything. Nearly all the content was new. The users were not unlike happy gardeners in a paradise. Some wanted to nurture rare orchids, some wanted to concentrate on farming food. Yet, everything was small scale. If a weed showed up, we had the resources to study it carefully. Painstakingly isolate it from the wheat and the orchids, try and mutate it to something more interesting. Failing that we would uproot it, by hand, so as not to disturb the plants near by. Some did not want to participate in that kind of gardening, but that was tolerated, because dealing with the weeds was not too time consuming.
When the site started growing, problems started appearing. Some would have liked to continue doing what they had always done. Others pointed out the benefits of crop rotation, pointing out that monocropping depletes the soil of some nutrients, making it less fertile for seasons to come, and also making it easier for pests to appear. Fights broke out. In the end some kind of a truce was reached. Even though there was some collateral damage, we still had enough resources to protect some of the useful plants that happened to be close to a weed.
But the site kept growing. Needing to feed a lot of people, we, almost without noticing exactly when the change happened, switched to intensive farming. We still want to do crop rotation. But, the scale has gone up. We no longer have the resources to carefully examine each and every plant by hand. Says Wikipedia: It takes very few wild oat plants to cause a significant reduction in the yield of a wheat or cultivated oat field, even though the seeds are a type of oat. So when we spot a few wild oat plants, severe collateral damage will be necessary. The farmer happily sacrifices many good stalks to make sure all the wild oats are destroyed. Whatever it takes to save the main crop.
So that's why many deletions in the current stage of the development of the site are IMHO necessary.
- The questions may be monocropping duplicates, or pests of attempts to outsource homework.
- Both of those must be stopped, for they will invite their "friends" to crash the party. If the price we have to pay is the destruction of a few correct answers, so be it.
But, that's not the end of it. What lies in the future? Reread Shog9's later post. Water. If we don't accommodate for it, it will destroy the farm. And. Water. Does. Not. Care. What/who is water here? Many interpretations are possible. His most important message may be (my interpretation) that we all need to brace for a future when we ALL need to compromise on some of our dearest principles. Linking to the infamous post describing four types of SE users
- The librarians may be forced to accept that they cannot have full control of the content. Some may leave the site in disgust, but do observe that the librarians will get reinforcements from the ranks of former prolific answerers.
- The noobs will also need to learn the site norms. But, the continued existence of the site needs new users. Many a noob will inadvertently start out as one of this type. But we need many of them to stay.
- The most knowledgable of the noobs will become prolific answerers. If left to themselves usually not adding new content. So they will need to learn to compromise. And, in the end, they will be converted to librarians (seen this happen a few times already)...
- ... or possibly to an apathic shaking their head on the sidelines (this fate awaits a few librarians also).
But, while all this played out, there was the hermit, happily tending to a few orchids. Not worrying about the ego points and politics. Just beautiful math. Very Zen (unless somebody steps on his orchids).