It just doesn't pan out in either direction. Section 31 didn't care about Odo and their act of genocide was, if nothing else, just as likely to prolong the war and make it bloodier as it was to end it more quickly. This unconscionable act, that could have easily cost the lives of thousands of more allied officers, can never be punished or tried in a court... because Section 31 has no masters and that is wrong.
As a point of clarification, there actually is no reason at all why Section 31 could never be tried and punished. Section 31 may answer to no one, but that doesn't mean they're not supposed to. As Federation Citizens, they are bound by the laws of the Federation and they are not above the law just because they say they are. I think it's more accurate to say that Starfleet and the Federation were unwilling to deal with the issue effectively and in many cases turned a blind eye to their activities. However, there is no reason to assume that the political situation in either Starfleet or the Federation couldn't change in such a manner that the Section 31 problem would be dealt with.
Well, to be fair, had it not been for the virus, Odo would not have had the opportunity he did, to turn the F.C. against her warlike ways.
For proof of this, note the last time the two linked. Odo hardly convinced her of her error.
It was only the desperation she felt--and the simple act of compassion Odo made--which had been taught to him by the solids--that caused her to change.
He would not have been able to commit that act...had it not been for the virus.
I'll give that the virus weakened her defenses emotionally. But the invasion of the Federation Alliance was seemingly going to do that anyway. She was in a desperate situation, virus or not, and that Odo wanted to link with her had as much to do with helping her understand solids as it did with curing her. Without the virus he could still have communicated that idea in the link. At some point he figured out how to do that and that's what he did that finally convinced her to end the war. She wasn't even going to link with him if there were terms involved.
I'm not convinced at all, nor am I really sure that anything shown on screen indicates, that Odo either turned the female changeling against her warlike ways, convinced her that the war was wrong, taught her what compassion is, or in any other way changed her opinion on solids or the war. I don't even think the cure was a major contributing factor to her surrender (though it may have helped).
The proof is in what Odo did next -- he returned to his people. The female changeling flat out told Weyoun that Odo returning to the Link was
more important to her than the
entire Alpha Quadrant. This is how Odo got her to surrender.
EDIT: My point here is that Odo knew this and made the bargain with her to return to the Link in exchange for her surrender -- that Odo could cure the Founders was a bonus. In my opinion, whether the Link was infected
or not, Odo would still have been able to get her to surrender just by promising to return to the Link.
^I am asking for a legal definition. We cannot put into law a judgement based on intentions, per se, lest we become thought police.
Legal definitions of criminal actions must usually, and typically do, depend a great deal on intent. As stated by another poster, it is the difference between premeditated murder and manslaughter. In fact, premeditated murder is almost entirely about intent. You don't get the death penalty because your brakes failed, resulting in you rear-ending and killing a motorcyclist.
Speaking specifically on genocide, The 1948 United Nations Convention on the Prevention and Punishment of the Crime of Genocide defines genocide as follows, and whether or not it is considered genocide hinges almost entirely on intent:
"Any of the following acts committed
with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such: killing members of the group; causing serious bodily or mental harm to members of the group; deliberately inflicting on the group conditions of life, calculated to bring about its physical destruction in whole or in part; imposing measures intended to prevent births within the group; [and] forcibly transferring children of the group to another group." (emphasis mine)
Laws which have intent considered as a factor are not laws against "thoughts."
They're not "thought police" unless they arrest you solely for
thinking about committing genocide.