Dreams are messages from the deep.

What the books make clear is that the Butlerian Jihad led to the banishment of all machines built "in the likeness of the human mind", which means that all artificial creations made to substitute human abilities, even basic computers and calculators, were not allowed anymore, so much so that literal human computers became a widespread necessity throughout civilization.

And just like Mentats arose in order to replace the old computers, the Spacing Guild must have been a replacement for some kind of navigational devices which coordinated interstellar travel for millennia before the Jihad, as is hinted at in one of the Dune Appendices.

My question is: if those machines were banned, why was the Spacing Guild allowed to navigate through the use of Holtzman Engines?

If the extent of the Jihad was to destroy navigational devices, which are not a crutch in the same way a calculator is, but are a necessary addition to human capabilities for the existence of an interstellar civilization, then why not destroy Holtzman Engines as well?

Or why was the Baron Vladimir Harkonnen allowed to use suspensor-nullification devices to sustain his weight, or for that matter, why was anyone allowed to use suspensors for easier transportation of objects when even navigational computers, which were very much necessary, could not be used?