well, it's definitely more fun, and rewarding, to play your own parts, rather then cutting and pasting them.
at least for me, it is.
i do use 'loops' (actually, midi clips) when building drum tracks in superior drummer, but i always deeply edit them to make them personal.
so, i cannot say that i'm a purist.
i DO use live drums whenever possible.....this is always preferable.
and i do like the idea of using loops as a writing tool, and the occasional 'Track-Guest star' for the odd sounds here and there..
but i have found that (in particular) 'FREE' loops, typically are very basic, are just plain weird, and do not have such good feel.
i think creating your own loops, taking the time to program them and give them a unique feel, should be the goal of loop users.