While I agree they needed the warrant in the first place, proponents would argue that they wouldn't have known about these guys without the program.
Given that these guys were arrested in the U.K. I don't know if the N.S.A. tipped off U.K. authorities, or if the program was entirely useless in this scenario.
Regardless, the real question is was this worth the liberties lost?
What liberties lost?
There aren't any laws protecting the transmission of Email, AFAICT. The analogy I use when explaining email to other people is that of a postcard; anybody who handles it (relay servers, ISPs, etc) can read it, but they *probably* won't. It's not like sealed postal mail, which I believe has some legal status.
If you want any security in your electronic communications, use strong crypto.