The question is complicated.

I can try to make a call on an act of violence and keep prejudice out of it.

If innocents were killed when there was no possibility of killing military or politicals and without the possibility of settling an issue, it is to me pure terrorism.

The question then becomes, when is terrorism ever justified?

Sherman committed terror (mainly against property) in the interest of settling an issue, as did the allies when they dropped the nukes in Japan and fired bombed Germany. Therefore you can decide for yourself whether it was justified.

The Irish mainly targeted the British military with much collateral damage, as did the Jews pre-Israel. Even in the case of the OC bombing the target was a government building. Again the incidents are subject to individual interpretation and moral judgement.

When an act targets a school bus or a resturant, it fails on all counts. There are no military or political casualties and it does not serve to resolve the issue. It only exaserbates the problem. Some will say that this is also a judgement call but I believe that a reasonable person can make reasonable moral judgements.

The key word is reasonable.