I mentioned the moral aspect because the only way the Alpha quadrant powers can effectively fight an enemy as massive as the Borg is to unite their forces.
Since the Klingon-Cardassian alliance is founded on the basis of brutality to other races,those same races won't lift a finger to save it against the Borg.
Let's say the Alliance wakes up and asks for help to stop the Borg.The other races may actually stand by to allow the Borg to do their dirty work for them by eliminating the Alliance for either revenge or 'the greater good' depending on which species you ask.
At least they'll see it that way until the Borg show up in their backyards,by which point it'll be too late.
No one in the MU will ever help the K-C Alliance. Even setting aside the fact that no one would want to in the first place (given how brutal the KCA is), the very concept of alliances and working together against a common enemy is utterly foreign to most races in the MU. Nobody would help the Alliance - or anyone else.
Hell, I'm surprised that even the MU Klingons and Cardassians are still allies. Alliances just don't seem to be in the nature of anyone in that universe.