They used false pretenses to engage in mere military expansionism against another sovereign state, one that had undergone a revolution that would have made them more open to diplomacy with the Feds instead of wanton death and violence. No, they weren't wrong.
First of all, we don’t know that there was any pretense involved. I think the Klingons probably did believe when the operation started that Changelings were positioning themselves to take control of the Cardassian Union. For that matter, just because the council members themselves didn’t turn out to be changelings doesn’t mean the Klingons were wrong about the coup being supported by the Founders as part of a strategy to take control of Cardassia. (Disclaimer: WOTW is as far as I have gotten. I don’t know what future episodes will tell us about changelings on Cardassia.)
As for military expansionism against a sovereign state that was poorly defended and ripe for the taking, that’s what empires do. They are the Klingon Empire
, right? Doesn’t the Federation treaty with the Klingon Empire give them a right under the treaty to be an empire? Hard to imagine the empire agreeing to a treaty that didn’t. (It’s even harder to imagine the Klingons being okay with such a treaty, which would make the Klingon’s eventual withdrawal from the treaty a practical certainty.) Presumably, the treaty would prohibit the Klingons from moving against space controlled by the Federation, Federation member worlds, or Federation protected worlds, but would allow some room for expansion, as long as the expansion is consistent with Federation interests. Granted, I’m just making reasonable assumptions because I haven’t had an opportunity to read the treaty.
As for Federation interests, does the Federation want Cardassian space controlled by Cardassians, who are hostile to the Federation, or do they want the space controlled by a Federation ally? I think the latter is better for the Federation, especially if the Klingons are correct about the Dominion’s involvement in the coup. When Gowron says, “All that matters is the Alpha Quadrant will be safer with the Klingon Empire in control of Cardassia,” he seems to be making a lot of sense.
By challenging the Klingon invasion of Cardassia, they not only kept that space in the hands of a hostile power, but provoked the Klingons to withdraw from the treaty with the Federation and the High Chancellor to declare, “The Klingon Empire will remember what has happened here. You sided against us in battle, and this we do not forgive, or forget.”
So, by doing nothing, Klingon space and Cardassian space would both have been controlled by a Federation ally. Because the Federation intervened, Klingon space and Cardassian space are both controlled by enemies of the Federation, and the prospect of a united Alpha Quadrant standing against the Dominion has become much less likely.
Gary Mitchell wrote:
In the episode they chose option #1. Did they make the right call?
I don't remember the UFP intervening militarily. I just remember Sisko helping to evacuate the Detapa Council.
The evacuation of the Council was a military operation. They came in with a warship and attacked and destroyed Klingon warships in order to facilitate the evacuation. When the Klingons pursued, it led to the confrontation at DS9, with Sisko turning the station’s military power against the Klingons, destroying at least eight Klingon ships, and had several Starfleet ships on the way for reinforcement.
With this show of military force, the Federation demanded the Klingons relinquish control of the Cardassian colonies they seized during the invasion. (Dax reported that the Klingons were “refusing” to do that, which suggests that the Federation made such a demand.) No two ways about it, that’s military intervention.