Real drone strikes are not as surgical as propaganda would have you believe. It is rather offensive to pass off the many murders by drone as mere surgical strikes.
Just as you have managed to convince yourself that this is acceptable, Liber8's members could have convinced themselves it was acceptable. Especially since, unlike drone strikes that constantly take out alleged key leaders whose removal never turns out to make a damn bit of difference, Liber8 really did take out a substantial portion of the ownership in hopes of making a difference.
Also, the implicit notion that Liber8 should have used its own drones is preposterous. Really, the reason for targeting the whole building is because the real target is so heavily shielded that only an indirect attack can succeed. The declaration there are more targeted methods available to Liber8 has absolutely no support. Outrage at questioning the surgical precision of drone strikes has clouded your judgment.
None of this means Liber8 is correct in its judgments, any more than condemning drone strikes as murderous means the targets are correct in whatever they are alleged to do. But it does mean that if you convince yourself the casualties are inevitable collateral damage, then it feels different from killing someone with your own hands.