The laws of that world, indeed. Which, yet again, are for the developers to decide.
And here is what they decided. From the codex:
Combat hard-suits use a dual-layer system to protect the wearer. The inner layer consists of fabric armor with kinetic padding. Areas that don't need to be flexible, such as the chest or shins, are reinforced with sheets of lightweight ablative ceramic.
The outer layer consists of automatically-generated kinetic barriers. Objects traveling above a certain speed will trigger the barrier's reflex system and be deflected, provided there is enough energy left in the shield's power cell.
Armored hard-suits are sealable to protect the wearer from extremes of temperature and atmosphere. Standard equipment includes an on-board mini-frame and a communications, navigation, and sensing suite. The mini-frame is designed to accept and display data from a weapon's smart targeting system to make it easier to locate and eliminate enemies.
on barriers:
Kinetic barriers, colloquially called "shields", provide protection against most mass accelerator weapons. Whether on a starship or a soldier's suit of armor, the basic principle remains the same.
Kinetic barriers are repulsive mass effect fields projected from tiny emitters. These shields safely deflect small objects traveling at rapid velocities. This affords protection from bullets and other dangerous projectiles, but still allows the user to sit down without knocking away their chair.
The shielding afforded by kinetic barriers does not protect against extremes of temperature, toxins, or radiation
So what you're saying is the armor is optional? OR maybe those tight suits are more protective than you assume. It's the future, good sir! FTL is preposterously unrealistic, as are omnisexuality, biotics and a dozen other things, but we have no problem accepting them because fiction.
But, our fashion sense shall not be fooled! Gods no!
How does Samara's cleavage protect her from any of the things I listed above? As I told you, Mass Effect set certain rules on how its universe works, in what kinetic barriers can protect against, and what it can't, which required body armor or "hardsuits" to compensate for.
"science fiction" is not carte blanche to just make cr@p up. True the outfits are among the least of Mass Effects sins (especially after ME3) but it's still a quite blatant one