They absolutely are terrorists.
The Japanese are doing absolutely nothing wrong. In fact if you were to actually look into the subject they have not broken any laws. There is a ban on whaling with the exception of scientific collection. Does the whale meat end up on dinner tables? Yup, but that's an addendum to the law, they are not allowed to waste the carcasses.
Now lets look at the pirates on whale wars. They are a small fleet of vessels with no national affiliation in international waters attacking, boarding and actively pursuing Japanese vessels. This makes them pirates.
Another term that applies to them is eco-terrorist. They use extreme action to attempt to reach a goal. For them it is supposed to be stopping whaling but lets be honest, its really just for ratings at this point. They aren't stopping anything. They are backed by a US television station and funded by organizations who have always supported eco-terrorism such as the murder of law abiding civilians as well as the illegal mass murder of thousands of cats and dogs, PETA.
Conservation issues are a huge mess and the only way to actively solve environmental issues is by having management that is backed by government and public sectors. When you support or actively involve yourself in eco-terrorism you blackmark your own cause and make it much less likely that it will ever succeed.
Much worse, people who are on the fringe about environmental issues get an even worse impression of the "moonbat hippies" that they envision when they imagine an environmentalist.
Whale wars is a blight on the environmental conservation movement and does more harm in the long run to the environment than it does good. Those people are not heroes. They are mislead and misguided attention seeking nobodies who don't understand the enormity of their own actions. To support them does nothing more than show your own lack of understanding of environmentalism and the world you live in.