I have some advice, but I completely agree with this guide. I was thinking about writing something similar myself until I saw this.
I have two suggestions: create an introductory summary (of a few sentences), and frame advice-giving as being in would-be ragers' self-interest. First, I suspect that many would-be ragers that need to read this guide are cynical people with short attention spans. I'm betting that many of the people that start raging at the 10:00 mark don't read past the introductory paragraph. As a result, it might help to make a "bottom line" early on in the guide that sums up your thesis in a few sentences.
Also, again, I think you need to frame your thesis as being in would-be ragers self-interest (and I'll explain why below). As for actual wording I suggest the following:
"Raging never helps, but advice sometimes does. If you give advice, the team might be able to turn around and win THIS game."
I talk with ragers a lot (perhaps because I'm a glutton for punishment), and I consistently use this approach. Believe it or not, this sometimes works.
I'll explain: in economics, a basic fundamental is negative versus positive externalities. When you do something good that affects other people as well, that creates positive externalities, and negative is vice versa. Almost without fail, actions that create positive externalities (in this case helping out "noobs") don't get done enough. [Side note: that's why the government has to subsidize activities that create positive externalities, like building roads and schools, to make sure they get done.]
However, while helping "noobs" does create positive externalities (it helps the noobs themselves and the community at large, which you point out), helping noobs is also in the would-be ragers self-interest. It's in their self-interest because sometimes a few pieces of carefully worded advice can turn around a game, and help the would-be ragers to get a win. This distinction between creating a "positive externality" and doing something in one's own self interest is an important one. Again, in economics, actions that are in our own self-interests traditionally do get "done enough", and don't have to be subsidized. While some people will create positive externalities just because it's "the right thing to do," unfortunately, I suspect that most ragers are rarely these people.
In other words, in order to get most would-be ragers to do anything, you have to frame advice as something that's in their own self-interest. The problem is that framing advice as "helping noobs in the long run" or "improves the community" doesn't make advice look like it's in ragers' self-interest. Instead, you have to communicate to them that giving advice might help them (the would-be ragers) directly. How? By communicating that advice could potentially help turn the game around for a win.
I haven't read all the comments, so I'm not sure if I'm repeating anyone. Also, I realize that most LoL discussions don't use economics and psychology, so everything may not have made sense. Please let me know if that's the case!