They were just as much under the stress, and in fact probably more so, than the traditional military. The fact that they were acting in a military capacity in a war zone is what is important. The fact that by name they were not the standard armed forces is minutia.
Methinks you're having some reading issues. The point, and the relevance, is that a mercenary force can be distinguished from a national military force because it lacks the discipline and training of an army. It is the discipline and training that is the primary factor in any military force retaining control of the battlefield. This has been the truth of warfare since it first began.
If mercenaries become savage beasts under pressure, this is merely strong evidence that they lack the training and discipline of a military force - which is incidentally one of the primary reasons mercenaries are banned under the International Laws of Armed Conflict.
The entire
point of military training and discipline is to
prevent soldiers cracking under the strain of conflict. Therefore your claim that you can't have homosexuals or women in frontline combat situations is really just a bold statement that the USA's military is severely lacking in discipline and training - a position that I don't personally agree with.
For the record, many military forces around the world don't have anywhere near the sort of restrictions on private relationships that the US military appears to have. Many military forces around the world allow women and homosexuals in frontline combat roles. Not only is this true today, but it has been true throughout human history. Funnily enough these military forces don't seem to have any problems with the performance of their forces.
Try to justify it all you want, when it comes down to it, the only
actual objection there is to homosexuals or women in the military is good ole fashioned yankee bigotry.
Given that the military's primary symbolic duty is to defend the ideals and values of society, it stands to reason that the military should be the
first place to abandon immoral, out-dated, and unjustified discrimination. Not the last. If the US military can't handle treating women and homosexuals the same as straight men, what does that really say about America? Nothing good.