Well, I see what you are talking about, but it's not that it's totally forbidden, WP:TERRORIST says "If a reliable source describes a person or group using one of these words, then the description must be attributed in the article text to its source, preferably by direct quotation, and always with a verifiable citation. If the term is used with a clear meaning by multiple reliable independent sources, then citations to several such sources should be provided in the sentence where it appears." so the issue is one of being absolutely certain that a reliable source described them in this manner. Al-Queda has an example of this, of course they've been called terrorists by lots and lots of sources, probably not the case here...