Well, my process of course differs slightly from page to page, depending on which medium I am using. But for my inked pages...
I ink straight onto my original pencils. I should mention that many people think this is a bad idea, but I find scanning my pencils, making them blue, blah blah blah to be way too much trouble. After I ink, I erase all the pencil marks. If you make only wide, dark lines when you ink, erasing probably isn't necessary. But if you, like me, sometimes use really tiny lines for details and the like, you will find that once you've adjusted the picture so that the pencil doesn't show, the skinny lines won't show very well either.
I scan in 300 dpi, greyscale. Once I have the scan trimmed down (I try not to draw too close to the edges of the paper), I reduce the resolution to 72 dpi and the size to 650 pixels wide.
In my opinion, adjustments to the picture can be made before or after you reduce the size.... rarely do I ever see it making a difference. I suppose, however, that it's better to do everything before you reduce... but that can be really slow if your computer's like mine. Anyhow, I clean up little errors with the eraser (I prefer to correct on the computer than to use white-out, which I'm bad at controlling and which usually shows up in the scan and has to be erased anyway). Then I make adjustments to the white really white and the black really black. Every image manipulation program has a brightness/contrast setting somewhere, so you can use that. What I prefer to use, however, is the "levels" tool--I dunno if it's called something else in other programs, but that's what it's called in GIMP. I move the far right slider toward the middle just a smidge (to get rid of any lingering smudges or pencil lines that didn't erase), then move the middle slider about 1/3 to 1/2 of the way to the right, to make the darks really dark.
And that's all I do. Sorry that ended up being such a long answer.... but I figured you probably were looking for details...
Even though I haven't seen your friend's artwork, or heard his argument, I think he's totally wrong.
There should be no problem.