It requires so much extra discipline to think for yourself and not use it, you will be forced to use it in your job or be seen as a Luddite and your ability to think for yourself in the domain will diminish over time - your domain thinking muscle will gradually atrophy from lack of use.
Why would any of us bother thinking hard, when there is no financial incentive to doing so ?
Your analogy fails with shovels and excavators .. because General synthetic intelligence is not a single purpose narrow 'tool'. near-future AI is equivalent to an alien intelligent species competing for resources, or equivalent to a cheaper smarter non-human 'outsource worker'.