The moral and legal liability has precise limits. No software application or payment service could be ever expected to prevent any and all criminal activity in relation to it's use. Google is on the hook, but to a more much limited extent than you suggest, namely they need to do their due diligence in providing a safe service, as far as it's reasonably expected, and inform the users as to the limitations of the service and that the other participants are not endorsed or vetted by Google. That is a level of risk and limited liability they can legally offer, because the much riskier anonymous hitchiking is generally legal.
Google is absolutely not responsible for the rapes and muggings perpetrated by users of Adwords or Waze.
If you or a family member used Waze Carpool, and got raped or murdered, are you going to sit there quietly and say "oh well, not Google's fault"?
As a engineer providing a software solution, it's great to sit in an office desk and say "there are precise legal limits", it's exact, precise, formal, and correct. Like a math problem almost. This is the exact line.
But imagine if you used somebody else's service, and you got raped. Or your family member got raped. Are you really going to not sue and let the newspapers know what happened? It's not just 1's and 0s anymore, it becomes a moral/emotional issue.
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.
Just because the law "precisely" says it's not the carmaker's fault, doesn't mean the carmaker is not "on the hook" or share some of the legal burden.
I am not saying that we should ban cars or ban carsharing. I am saying, if you offer carsharing as a software service, and something goes wrong during that service, you are involved legally. It's not a precise "on/off" switch like launching a software product.
The point I'm driving at is that it's still a marketplace and it comes with all the same standard hazards that apply to any marketplace. There are disputes and exceptions that have to be managed. Machines are not good at that yet.
Setting the support obligation or morality questions aside for a moment (though I'm on the side of "by facilitating and profiting from this, you accept some responsibility for the quality of that facilitation"), that big difference is still critical: suing the operator of a neighborhood carpool mailing list or somesuch has limited yield. Suing Google has potentially massive yield. So a corporation should think about that sort of risk, just like they would the PR risks, etc, of letting it be an unregulated wild west.
Your position sounds a lot like "light or even largely-community-based self-moderation will be enough" and yet platforms like Twitter and Reddit that have attracted some large controversies and PR shitshows even without real money or real physical harm being involved. Heck, "don't read the comments" is standard internet advice to the point of being cliche.
This is something only an engineer would say. In the real world, once you provide a service, you absolutely are on the hook— both ethically and in the mind of the average consumer— for providing some level of service when it goes wrong. “Don’t like, don’t use” is not an acceptable answer, especially in a business like this where outcomes like robbery, rape, etc. are all possible.