Actually, I'd think the last thing the Federation - Earth, in particular - would need, is for hundreds or even thousands of Borg-victimized races to come banging on their front door looking for revenge. (You think Andorians, for example, would be all that happy about learning that a fellow member of the Federation was indirectly responsible for what happened to them?) If it takes a few secrets to stop that from happening, I'd call it even.
I think the Andorians are mature enough as a society to know better than to blame an entire species, and a loyal ally and partner in the Federation, for the actions of a few isolated individuals in the distant past.
We all know what Andorians are like. They are warlike, impetuous, hotheaded, and militaristic. Look at Shran, for example. Just think of what somebody like him would do if he were alive today and found out that humans, however accidentally, played a large part in what was essentially the destruction of his homeworld.
To put it another way: Look at how people like Archer and Trip reacted when they found out about the Xindi attack on Earth. And then multiply that by, oh, a hell of a lot. (Remember, the Xindi attack 'only' killed a few million people. And if humans can react with such rage and grief, how do you think *Andorians* would handle an attack that was much WORSE?)
And if you still need further convincing: Look at the lengths Section 31 went through to cover up the events in A Time To Kill/Heal
. Do you think the Klingons should learn the truth about *that*?
Indeed, it might be much worse for the Klingons to find out about humanity's role in the creation of the Borg. I think it's fairly safe to say that more Klingons died at Borg hands than at Tezwa...and if Section 31 was as insistent on keeping the Klingons from finding out about some namby-pamby alien PM destroying a few Klingon ships, how do you think they would feel about letting the Klingons know about humanity being the origin of the Borg, who killed *millions* of Klingons? Somehow I doubt the Klingons would care that the Borg were an accident any more than the Andorians would, and probably a lot less. (We've all seen how little it takes to provoke a Klingon into fighting.)