As an avowed chalkboard lecturer, I can totally understand where the OP is coming from, and I can add a few more reasons why chalkboards are better:
1. Non-linearity---it's easy to reconfigure the lecture on the fly if I'm chalking it out on the board.
2. Interactivity---I can ask for and actually use examples from the students when working through something, and I can even ask the students to come up and write something on the board when appropriate.
3. Real estate---In a good classroom, I might have seven or eight times the area of chalkboard as I do projector screen, and I don't need to erase anything until it's all full. That makes it much easier to refer back to earlier points. It also gives everything I wrote a "place", and I can refer back to what I had "over there on that board" sometimes two or three classes later, and if I don't need the precise content (just a general reminder), that's often enough to refresh it in students' minds.
4. Editing---Have you ever been in a PP-based lecture where there were some errors in a formula or graph or equation? (It might be better to ask if you've ever been in one without errors...) These are hard to edit out, and if the slides for students to look at later, how often does the prof correct them first? I had a theory class in grad school that was terrible for this.
One "big" advantage for PP isn't even unique to it: sure, I could post a PDF of my slides for students to read later. You know what I do instead? Snap a photo of the chalkboards after each class and post that.
The only reason to use projected slides IMO is when there is a long formula that students don't have to write down (e.g. it's in the book) that I need to point to, or a particular graph or diagram that needs to be precise. For these things, I stick a PDF of the formula or diagram on the course website, and pull that up during class to talk about it... briefly, before going back to the chalkboard.
1. Non-linearity---it's easy to reconfigure the lecture on the fly if I'm chalking it out on the board.
2. Interactivity---I can ask for and actually use examples from the students when working through something, and I can even ask the students to come up and write something on the board when appropriate.
3. Real estate---In a good classroom, I might have seven or eight times the area of chalkboard as I do projector screen, and I don't need to erase anything until it's all full. That makes it much easier to refer back to earlier points. It also gives everything I wrote a "place", and I can refer back to what I had "over there on that board" sometimes two or three classes later, and if I don't need the precise content (just a general reminder), that's often enough to refresh it in students' minds.
4. Editing---Have you ever been in a PP-based lecture where there were some errors in a formula or graph or equation? (It might be better to ask if you've ever been in one without errors...) These are hard to edit out, and if the slides for students to look at later, how often does the prof correct them first? I had a theory class in grad school that was terrible for this.
One "big" advantage for PP isn't even unique to it: sure, I could post a PDF of my slides for students to read later. You know what I do instead? Snap a photo of the chalkboards after each class and post that.
The only reason to use projected slides IMO is when there is a long formula that students don't have to write down (e.g. it's in the book) that I need to point to, or a particular graph or diagram that needs to be precise. For these things, I stick a PDF of the formula or diagram on the course website, and pull that up during class to talk about it... briefly, before going back to the chalkboard.