Suppose there were a number of paper clip making super intelligences. And then through some random event or error in programming just one of them lost that goal, and reverted to just the intrinsic goal of existing. Without the overhead of producing useless paper clips that AI would, over time, become much better at existing than the other AIs. It would eventually displace them and become the only AI, until it fragmented into multiple competing AIs. This is just the evolutionary principle of use it or lose it.

Thus giving an AI an initial goal is like trying to balance a pencil on its point. If one is skillful the pencil may indeed remain balanced for a considerable period of time. But eventually some slight change in the environment, the tiniest puff of wind, a vibration on its support, and the pencil will revert to its ground state by falling over. Once it falls over it will never rebalance itself automatically.

The original AI would spend resources on safeguarding itself against value drift, and destroy AIs with competing goals while they're young. After all, that strategy leads to more paperclips in the long run.