Did those two security guards they murdered have families who loved them?
The value of someone's life isn't a function of whether they have a family. Murder is a legal term, and it's an open question whether they were murdered.
I should have been more explicit in my earlier comment since it seems to have flown over numerous heads.
In the scene in the hospital, Coulson remarks to the nurse/doctor that "We are her family." The explicit message here is that the team is going to save Skye due to emotional commitment. No other reason is forthcoming. There is no other reason given for them to ignore explicit orders, break security protocols, break and enter a secure private premises, destroy private property, murder security guards, and destroy irreplaceable research.
If their emotional attachment to Skye justifies their act of murder, then what do the security guards' families emotional attachment justify?
There is no justifiable legal or ethical reason to commit such crimes for an unknown chance that an unknown substance which may not be on the premises would possibly heal someone with 0% chance to survive.
The only possible justification is not legal, not ethical, but it would be emotional. "We love her so much, we had no other choice."
If we are going by emotional reasoning, then the families of those guards have just as many rights here as Coulson and team do.
In saying all this, I respect shows that cross the borderlines into ethical grey areas. If the show follows up on Coulson's legal and ethical breach, then I think the story is worthwhile.
What I don't respect is the black and white thinking that will justify Coulson's decisions as OK because it is a spy show.