For better or worse, the removal of that one individual hadn't altered the timeline except for their absence from it. Obviously the deaths of billions of people is a different matter.
Also, saving those billions of individuals would most likely result in a galaxy ultimately controlled by the Borg. How exactly is that a victory?
A galaxy ultimately controlled by the borg? Hardly.
I can easily come up with a way to save an arbitrarily high number of people without changing the past in any way.
Simply use a temporal transporter (a technology shown in TNG) to teleport all the billions who were about to die from a millisecond before their death to their future (your present).
Of course, the reasoning behind the DTI's categorical refusal to save billions was not the impossibility of doing it without undesirable consequences, but the fact that that would constitute changing the past (and not changing the past was shown to be the de fato religion of the DTI agents - the logical justifications of this credo being quite thin).
Until one of the DTI's own was to be saved, that is; then the refusal was not even close to categorical.
As per the DTI agents' behaviour, all people are equal, but some are more equal than others.
As said - elitist a$$holes.
[..]the judge and the jury?
The DTI certainly do think they are so.
[..]Do they have armed guards placed behind the backs of all DTI workers, with the fingers on the triggers[..]
Except there are no such guards (or they are utterly/absolutely undetectable and never do something regardless of the situation).