It's a tunnel into your internal network.
If nation states and/or cyber criminals do control most of tor, then you are opening your internal network to those groups.
If nation states and/or cyber criminals do control most of tor, then you are opening your internal network to those groups.
It is also extremely likely that said adversaries control most of Tor, considering that the main mechanisms of tracing Tor circuits do not require control over any nodes of the Tor network whatsoever- snooping on IXPs and as many autonomous systems and underwater wires as possible.