I can understand ripping sprite for own learning purposes, to see how characters are animated (walk, run, jump) or how diferent objects are drawn so you could use that knowledge to make your own sprites, but using someone else graphics for your own game it's just lame, and even after that saying you are making a fangame it's not that cool at all .
To be honest i don't realy understand that fangame idea...our world don't need another 10.000 Mario Bros or Megaman fangame-rip games...but it's only my opinion.