Why did whately (and probably most other english officials) feel that the american colonists should be willing to pay higher taxes to parliament?

They felt that it was the parliaments right to tax the colonies.

Moreover, after the French & Indian War (7 Years War), Britain was drowning in debt and felt the colonies hadn't been contributing much to Britain's affairs which was, in a way, true seeing that the colonies were under the policy of salutary neglect for a long period of time in which Britain had very loosely enforced parliamentary laws in order to maintain colonial obedience to the Crown. 

Where’s the diagrams?