First of all: This is my opinion/view on this.
About the voice lines.
Aren't the security forces supposed to be professionals or experienced? They handle guns, call in support and use military phrases and whatever, but as soon as a bullet flies by they seem to sh** their pants. All the whining and complaining, especially the female shrieking sometimes, it really weirds me out.
Realisticly, this is really dumb, it would just give away your position. Soldiers in documentaries I've seen are able to stay calm and observe the situation.
The Insurgents scream too when in danger, but in a way that is way more "hardcore" and fitting in general.
Oh and they all have those neutral facial expressions like they've never seen combat before. I look more battle hardened when I wake up in the morning...
It just feels like I play as/ and with a buch of wussies when playing security. I really like the Insurgents tho.