One of the features of a properly tuned fountain pen is that require zero friction or pressure to write. The reason for this is that they transfer ink to paper via capillary action so mere contact should be enough to put a line on the page.

I can't say erasure is a typical ability in fountain pen inks. In fact if you look into Noodler's Inks (two of the rollerballs mentioned come from Noodler's Inks) you'll notice that the creator of those inks leans the other way, toward forgery-proof, water-proof, tamper-evident, archival-quality, fade-resistant inks. Use those, and you'd be able to prove that you wrote it, and no one would be able to alter it.

That said, Noodler's provides "waterase" inks for use on material like whiteboards. Wipe the text away with a wet cloth.

I've recently taken to using a TWSBI Eco (fine) at work for note taking. I write maybe two to three pages a day. What amazed me about it is that the nib felt like using a pencil! It is tuned to run smoothly across the page, but provide a very subtle feedback to give it that feel.