They want to bring order. Their order. And this time it will not be the democratic treehugging niceasking national rights approving type of order. EVERYONE is to find THEIR place in the system! The system that the Sith make.
What has the republic managed to do in its 23000 years of existance!? Nothing!
The hutts are still vile and disgusting and corrupt. The republic has no controll, corruption spreads wildly amongst the planets. Rich trade groups grow ever more powerfull and there is NO respect for ANYTHING.
Only once the whole of the galaxy is brought under imperial rule and imperial systems will the galaxy be as peacefull as it should be. Ofcourse sith infighting will happen, but due to the sith way of life there will allways be competent sosiopaths at the top that can actually rule!