For example, do you trust SpaceX to not relay your location to your enemy? Do you want to broadcast your identity at all if there can be a man-in-the-middle-attack? A dozen other reasons....
A military service would probably use wider beams coming from the satellite, as well as different encryption (making it impossible to distinguish which terminal is being transmitted to on which beam and not using correlatable identifiers on unencrypted protocol layers at all).
Using civilian communications technology like cell phones has been a bad idea, as evidenced in the same conflict.
Use Starlink dishes as phased array point to point links across 500 km without the v2 Satellites?
There are 200 Ukrainian drone startups alone, many more in other countries. They all hack firmware. Hacker News readers should not be surprised.
If the protocol requires you to reveal your precise location to the network (so that satellite beams can correctly target you), how would you get around that using your own open firmware/hardware?
The same goes for authentication using (potentially) long-term stable or even public identifiers, as is the case for e.g. the IMSI with GSM (not sure if later 3GPP generations finally fixed that): A GSM network won't let you attach without revealing your IMSI over the radio interface at least once. You can spoof it, but then you won't get any service.
> Use Starlink dishes as phased array point to point links across 500 km without the v2 Satellites?
That's a completely different scenario than the one we're talking about here ("why can't military users relatively easily put some distance between the Starlink terminal and its users in a warzone?"), and one which I'd assume the military to have existing solutions for.
It would be dwarfed by the emanations from the, you know, space transmitter co-located with it. Locating the dish isn’t the issue, the proposal was using fiber to make the dish (detectable) and the operator (vulnerable) separated by distance.