Marcus was silent for a while, trying to determine Elizabeth's plans but here she was...he hated to admit it but she was right. The giant tanker could help however the last time a "machine" which turned out to be the good guy walked into a Resistance base without good intentions, they got strapped to a nuclear silo and shot at.
True, he remembered that but it wouldn't stop him from helping both and making a good ally.
"If we bring that tank, we risk it losing control in the base and potentially causing more bad than good. I know this Skynet has no idea about us here. But there's no telling how long your hacking job worked on the tank."