Probably, they are being chased by time. As they will try best to reach the time machine as soon as possible, afraid that it might possibly get destroyed by the usurpations. Or even worse, being used by them.
(As we seen some of the Usurpation Destroyers on the facility at level 41, which where the time machine being in it...)So they pretty much have no choice but to push forward using any methods necesary to reach the time machine in time. And like what Ayano said, the CS at that time doesn't know what Marine & Noir is. And might confirm them as an unknown hostile threat.
Also, it might be a silly decision for Marine & Noir to reveal themself to the CS on their true goal & identity. As the CS had no clue & evidences at all about them.
(Becuase they come from the future...)For example :
- Marine : Don't shoot! I'm from the future!
- CS lite 1 : Dude, you heard what this guy said ?
- CS lite 2 : Impossible!
- CS lite 3 : His probably some crazy dude who got brainwashed by the aliens xD
- Marine : NO it's True! I'm come to save the humanity!
- CS heavy : His crazy alright, let's just capture it & take him to the base.
* Marine being captured & being interogated, possibly become a experiment subject in the CS laboratory facility or being taken away to the mental hospital *