Doesn't even have to be political. Moneyed interests and fanboys and cultists use Wikipedia for PR and similar all the time. See Falun Gong, for example.
There are also groups of Wikipedia "editors" who coordinate off-wiki to influence its workings. (Sock-puppeting and meat-puppeting)
Even if we disregarded all the malicious actors, harmful incompetence is rampant on Wikipedia.
And I was just talking about the English Wikipedia here, there are many "small" Wikipedias which are much much worse.
I haven't checked the page on Falun Gong for some time, but there was a concerted and largely successful effort to depict Falun Gong as in its own propaganda on many related Wikipedia pages. Some related info:
This is just an example of the issue of Wikipedia processes being too vulnerable to abuse, in contrast to the rose-tinted glasses view that most HN commenters view Wikipedia.
The obvious reason for this in this case is that people interested in contributing to articles about the Falun Gong are mostly already followers of Falun Gong. Stuff like this is all around Wikipedia. A related issue that I already indicated in another comment here is how most well-meaning contributors very soon learn to keep off certain controversial or well guarded pages, because it's simply not enjoyable to constantly fight over the content. The fact is: resolving disputes takes much time and usually the party with more time on their hands and more "meat-puppets" and allies wins. Also, making enemies from among the "editors" is both unpleasant and inconvenient for possible future efforts on Wikipedia.
One other reason for this is that discussion threads on Wikipedia can become incredibly large and involved very quickly. Typically a comment on Wikipedia will reference "diffs", which are changes elsewhere on Wikipedia (each with their own context and possibly requiring domain knowledge to understand them), or they can reference actual off-Wiki sources (e.g., a published book). Then someone else will respond to that comment with references to other stuff, and soon it is simply not manageable to keep track of everything. Everyone only has a fixed amount of free time and attention span, so very often things which shouldn't be taken at face value are taken at face value. On the other hand, meticulously checking something argued in bad faith expends time that could have been spent elsewhere. Walls of text and deep chains of references will scare a proportion of people outright before even engaging the discussion.
Another reason is that the assumption of good faith on part of the contributors is deeply embedded in Wikipedia. Not assuming good faith is actually forbidden on Wikipedia, and this is enforced. This might sound like a good idea (maybe it even is a good idea, it's hard to say), but in effect it just adds to the complicated minefield of vague rules breaking which can get one sanctioned on WP, but it isn't clear it actually does anything to improve the (low) standards of discourse on Wikipedia.
Apart from the rule that everybody has to assume good faith, the Wikipedia processes themselves are built on the assumption of good faith: the idea with Wikipedia is that everyone can talk out the differences in their opinions to establish "consensus",[N0] but malicious people can be severely disruptive in a discussion without doing anything that would cause them to be punished in any way on Wikipedia. E.g., someone makes a misleading comment (perhaps by taking things out of context, perhaps by exploiting some subtle semantics) and now people have to respond to them, which can take much more effort than it takes to make those comments. And there are accounts which do this all the time.
Another (smaller, perhaps) issue, which is actually fixable with better tech, is that although Wikipedia discussion threads usually logically have a tree structure, in actuality it's all unstructured Wiki-markup. This means that it's possible for the tree structure to become malformed, causing the discussions to become even less readable. Even if everything is structured correctly, it's often difficult to tell where does a comment end without reading it in its entirety, which is again caused by the lack of structure in the comments, every Talk page is just a single blob of Wiki-markup editable by any participant.
Thus, if you want to disrupt Wikipedia, the real way forward is not vandalism, it's arguing in bad faith with inpenetrable walls of text while being "civil". Bonus points for finding comrades to help you in a concerted effort.
Changing anything can be a tremendous effort on Wikipedia, but trying to change something while being opposed by an organized (off-wiki) and vigilant group, especially if they are malicious... I fear the whole project simply does/will not scale because of this. Organized groups will sadly keep their control of some topics/pages, and my fear is this situation will only get worse as Wikipedia's scope increases.
[N0] What consensus actually means on Wikipedia is another issue entirely, and it's often completely abitrary - whoever happens to "close" the Request for Comments (RfC - the process used for "determining consensus" on Wikipedia) can effectively create the "consensus" themselves.
There are also groups of Wikipedia "editors" who coordinate off-wiki to influence its workings. (Sock-puppeting and meat-puppeting)
Even if we disregarded all the malicious actors, harmful incompetence is rampant on Wikipedia.
And I was just talking about the English Wikipedia here, there are many "small" Wikipedias which are much much worse.