1. Find a toilet
2. Open the door
3. =(
4. Look for a bush instead...

It's not a weewee-poopoo joke request;

I think the OFP+ArmA series have achieved what's best around for military assault simulation, and they have simultaneously achieved a great DIY survival simulation when even the tiniest rock/bush/tree to hide behind can save your life.

Since your visibility goes in pair with your survival - as in being seen before seeing usually results in a bad case of the deadies - any mean to hide yourself is welcome, including counting on your enemy's confidence to omit checking every hiding spot.
If field toilets become enterable, please don't turn them into man-sized bunkers... this is just a tactical issue related to line of sight and player assumption.