Anselm relies on the, as stated, "one-over-many principle". While there may be issues with that principle, it is nothing like the claim that "everything has a cause" (unless I suppose you mean to include formal causes, though this isn't quite right either).

Yeah I know that no theistic philosophers has made this stupid argument but when my teacher presented it to the class she claimed not only Anslem did Aquinas did as well when he clearly stated in Summa Theologica(or Contra Gentiles) that this was not the case. I tried to tell her and the class this was a strawman but no one believed me.

Wut? Here are two versions from the SEP:

Version A:
1. Whatever I clearly and distinctly perceive to be contained in the idea of something is true of that thing.
2. I clearly and distinctly perceive that necessary existence is contained in the idea of God.
:. Therefore, God exists.

Version B:
1. I have an idea of supremely perfect being, i.e. a being having all perfections.
2. Necessary existence is a perfection.
:. Therefore, a supremely perfect being exists.

Whatever objections might hold here, there is no even minimally sane, let alone charitable reading of these that might either construe or derrive "everything has a cause" as a premise.

AKG wrote:

@Mysterious Brony
In my case it was in a highschool TOK class with a non-philosopher teacher, but the fact that you encountered this strawman in an actual philosophy class makes me worried about the status of modern day philosophical academia. In fact before I graduate I'm going to make a powerpoint for all my TOK teachers about the cosmological arguments to show them what it actually says and so they don't repeat this bull to future students.

Well, firstly, don't get the impression that philosophy professors will always teach natural theology caricatures. As far as I am concerned, any philosopher can make mistakes regarding someone's position. Secondly, I remember taking an intro to philosophy class in some other secular college and the Thomistic arguments (Second Way) were treated more fairly. I think the professor embraced a secular worldview, but he seemed like a nice guy and was more balanced than other secular philosophers.