For that matter, every user of Tor is in the same situation.
But the premise is wrong. The police can investigate you as much as they like, they just can't assume that the traffic coming from that IP address has anything to do with anyone in particular.
You're still going to jail when you buy something with a stolen credit card and have it shipped to your house, regardless of whether you used Tor or operated a Tor exit node or are an ISP and used an IP address assigned to a customer.
ISPs have a specific set of statutes that grant them immunity as long as they comply with certain requirements [1]. Individual users do not.
Imagine me as the friendly neighbourhood trickster living on the same floor as you.
I buy an illegal firearm with a credit card bought over a DNM using Tor and have it mailed to your house.
Enjoy your preordained jailtime.
(you are not your address, IP or postal)
We don't prosecute the Department of Transportation when someone transports several hundred million dollars of cocaine across their roads.
Why should we treat digital highways, overpasses, and offramps, any differently?
An exit node operator isn't the sole user of the IP address they're assigned either. Yes, they're the only available suspect, but that doesn't change the fact that it's based on outrageously flawed evidence -- it's basically one step up from a hunch, and I don't think it's nearly good enough to be kicking someone's door in.