Could ask the same question to an auto engineer who's relative dies in a car crash. Should he quit his job, should we ban cars?
While auto safety is important, cars save much more lives than they take - and the economic opportunities they enable drastically change the median quality of life in societies where they are used.
In the same way, carsharing is not an enabler of crime, it's much safer than hitchhiking and would be a drastic improvement in the lives of people who are economically dependent of hitchhiking.
A good example is the Highway of Tears murders - in the last 40 years 20 to 40 women disappeared or were found dead hitchhiking the same stretch of highway in Canada. They were typically underprivileged and of aboriginal origins, and lacking other forms of transportation. The vast majority of cases remained unsolved.
Should something like internet carsharing had been in use by a victim, the police would have had acces to a vast trove of forensic data, including their last match to a known Waze user, identified by credit card, phone fingerprint and cell tower and GPS location history, as well as the victims own location trail up to the point where her phone is taken away/shut down. While a determined high tech killer could operate with these constraints, it's orders of magnitude more difficult. A determined killer is by definition unstoppable by any service or company.