Are rats rat-maximisers and are humans human-maximisers? Humans think they are the best thing in the world but they are also intelligent thus they realise it is counter-productive to turn everything into humans. We protect other species and we protect the environment (increasing levels of intelligence entails better protection). The amount of cockroaches, rats, and humans is not overly problematic. A sentient paper-clip making machine would also not be a problem. Proficiency in making paper-clips would increase in tandem with increased intelligence thus the increased intelligence would allow the paper-clip maximiser to see how it is senseless to create endless paper-clips. Really it is an utterly implausible scenario that a truly dangerous paper-clip maximiser could ever exist.