According to Craig Calfee there's nothing available at your local hardware store that will damage a carbon frame (at least no fluid). Mt experience starting with the first gen Specialized Allezs agrees with Craig's statement. Grease might leave a stain, might make slippage more likely, might require greater torque for binder aspects (which also speaks to the component's material) but will not harm the carbon's matrix, strength or laminations.

The more recent (then the early versions of carbon frames which often used AL interfaces with components) designs have more limiting torque levels of their binders and other interfaces. So using a carbon paste with a "grit" helps to contain the component, reduce the clamping or press in pressure and also reduce the galvanic reactions.

Carbon is electrically conductive enough so that other metals can and will galvanicly react with it. This is why when an AL insert is bonded to the carbon it needs some sort of insulation coating it (a layer of fiberglass is a common technique). (The early Specialized Allezs had a production run which failed to do this properly and had a high bonding failure rate). The carbon paste acts as a insulating barrier.

At work we now use carbon paste on all posts and many other clamping spots involving carbon to metals or carbon to carbon. Andy.