Years ago, when I was student teaching, during one of our weekly meetings we had a resume workshop. A few of us (myself included) volunteered our resumes so that we could discuss formatting and specific information that should be included, as well as strengths and weaknesses.
Mine was reamed. It was reamed because it was more than one page long.
Both the professor and another student (a graduate student who had apparently worked in the employment industry previously) felt that a one-page resume would be sufficient, especially for someone whose career was just starting. I agreed - but noted that I had nearly an entire page of conference-related activities that I felt were important to include. After all, I wanted my potential employer to know that I was actively involved in my profession and interested in developing professionally. There was no real counter-argument to that, only a reiteration that resumes should be one page because there are so many applicants, that anyone going through a thick stack of interested employees isn't going to want to read a second page. That might be true, I remember arguing, which is why the more relevant information, such as education and related employment history, is on the first page. I wasn't going to not include what I thought would be pertinent information simply because it didn't all fit on the first page. Furthermore, what does one do if one has a lot more professional experience? Simply leave it off because their decades of (in our case teaching) experience can't fit on the first page, despite its relevance? What about a career changer, someone who worked in one industry for 20 years but then decided to go into teaching? Perhaps they had related relevant experience that would be prudent to know. Leaving extensive experience off that resume is tantamount to that work never having been done.
(I was placated when one of the graduate students, in reading over my resume, said in a somewhat hushed tone, "I can't compete with this." And that was a point, too; I wanted to illustrate that I was more actively involved earlier in professional development than many of those who would be applying for the same position.)
Admittedly the professor was quieter than the graduate student, but I was annoyed at their inability to differentiate between someone whose career was just starting and someone who had more professional experience. I was 30 by the time I was student teaching, older than most in the class (including the graduate students), and having worked in various jobs before enrolling at Stony Brook University, I could foresee someone asking what exactly I had been doing with my time in the 12 years since I had graduated from high school.
I thought about that resume workshop this past week. I was at South Hills Middle School (the school where I had had a three-month subbing gig last fall), where I had an interview scheduled for an assistant reading teacher position. I was interviewed by the principal, J., and the assistant principals, M. and D. M in particular just went, "Wow, look at all her publications!" (I don't have any publications; those were conferences I'd attended and either presented at, or sessions I had chaired.) Nevertheless, including that list was increased their opinion of me. I was offered the job because I was so much more qualified than the other applicants.
The advice of only using a one-page resume is simply not good blanket advice; there are too many other factors to take into account much of the time