My issue with deontology-as-fundamental is that, whenever someone feels compelled to defend a deontological principle, they invariably end up making a consequentialist argument.

E.g. "Of course lying is wrong, because if lying were the general habit, communication would be impossible" or variants thereof.

The trouble, it seems to me, is that consequentialist moralities are easier to ground in human preferences (current and extrapolated) than are deontological ones, which seem to beg for a Framework of Objective Value to justify them. This is borne out by the fact that it is extremely difficult to think of a basic deontological rule which the vast majority of people (or the vast majority of educated people, etc.) would uphold unconditionally in every hypothetical.

If someone is going to argue that their deontological system should be adopted on the basis of its probable consequences, fine, that's perfectly valid. But in that case, as in the story of Churchill, we've already established what they are, we're just haggling over the price.