I am a fountain pen enthusiast, or I should rather say "used to be". If any effect Internet has had on my fountain-penmanship or any penmanship it has resulted in drastically decreased usage. Isn't it a general phenomenon? (I've no data on it, just what I have observed around me)

So if you meant just buying, selling, collecting, swapping pens, and talking about fountain pens then it makes sense (which is what it seems you have focussed on in your comment), but if that also involved actually using them then, I would say, overall the Internet has instead done great harm to it.