That's where Clippy might fail at viability-- unless it's the only maximizer around, that "kill everyone" strategy might catch the notice of entities capable of stopping it-- entities that wouldn't move against a friendlier AI.

An earth originating paperclipper that gets squashed by other super intelligences from somewhere else still is very bad for humans.

Though I don't see why a paperclipper couldn't compromise and cooperate with competing super intelligences as well as other super intelligences with different goals. If other AIs are a problem for Clippy, they are also a problem for AIs that are Friendly towards humans, but not neccesarily friendly towards alien super intelligences.