They are probably conflating GPT with UEFI with SecureBoot.
(and the reverse with MBR and Traditional-Bios and No-SecureBoot)
Despite these all being slightly different things.
And then we get back to very non-technical arguments around the topic.
Really, if you are comparing security its quite simple - Traditional BIOS offers no security. UEFI provides multiple advanced security options including checking firmware and driver signatures, as well as the ability to run anti-malware operations from outside the OS.
The counterarguments will be a mashup of tired old scaremongering about how ‘msoft runs the secure boot game in order to stop linux’ and some hand-waving about ‘bootkits’ that doesnt align with reality.