Sometimes it is justified.
It is never okay or justified!
Only if you're the christian god
Every revolution could be called "terrorism". So, absolutely it can be justified.
It depends on what you mean by terrorism, and what is the cause its being used for
It can because "One man's terrorist is another man's freedom fighter". The label of a "Terrorist" is just given out from a certain view point, and does not tell the whole story. Also many people throughout history have done far worse e.g. Genghis Khan and Joseph Stalin. It is easier to label people "Terrorists" than to understand why they do what they do.
No matter how much you hate someone, it is never ok to attack them like that.
http://www.washingtonsblog.com/2012/08/is-america-the-worlds-largest-sponsor-of-terrorism.html Even though America is a nation that LOVES terrorism, it's wrong and is not okay.
Definition: the use of violence and threats to intimidate or coerce, especially for political purposes. Attacking or hurting someone is not terrorism, that is violence.