Undertone wrote...
No it shouldn't be. Humans are always capable of having redeeming qualities or actions right there at the end when the scale is different and the perspective is changed, when you have it all into retrospect.
And it is exactly there where the evil or anti-heroes shine. Because sometimes you need evil to fight another kind of evil for an ultimately good purpose. And an "evil" character is just as capable of sacrifice as a "good" character. Just as a "good" character is capable of atrocities.
People are incredibly one sided and foolish if they think we are consistent with what we do. Because we are anything but consistent. Even the most cruel person would do something altruistic with the right emotion played or for the right cause.
To have morality choices restricted by consistency of actions is ridiciluous.
Uhhh I suppose that makes me idealist at the end. Naaaah, who am I kidding. 
Shepards is a pre-generated character, as such there is no wrong choice. But doing certain things will cut out certain choices.
In a more traditional RPG you should already have a "persona" for your character and the options simply give you the "best fit" to project that during play. However when a character is created specifically for the game,like Shepard. Anything fits, even if it seems widly against type. Because Shepard can't be wrong.
In the case of the high end choices it's perfectly clear than only the most dedicated P/R Shepards get them.
I almost always have problems with the Miranda/Jack fight, Zaeed as a Paragon, Morinths charm,Aasari spec.
Re-specing to the 100% profession option normally sorts it out. So it's not like you don't have ways around it most of the time. That extra 30% can make a huge difference in what options are open. Why else would there be a choice between one skill that caps at 70% (usually with more useful powers) and one that caps at 100%?