Could cryptocurrency "insurance" slow Bitcoin adoption?
If anything, I believe the ability to buy insurance on cryptocurrency investments would speed up adoption by making it less risky to traditional investors.  Simply having insurance available doesn't mandate that everyone buy it; we'd all still have the choice whether we opt-in or not.

Traditional investments tend to have insurance policies on the insurance policiy of the insurance policy of the initial investment.  While it's a somewhat yucky business, it's also a standard practice in today's financial ecosystem.  Having these options available for bitcoin only strengthens bitcoin's value proposition and familiarity to traditional investors.