They could be used to assassinate evil people, like Isaea and his father, which is doing good, measured by the absolute scale. To the class itself I'd give a chaotic neutral connotation. Assassins can be in service of the law officially or for their own sake, especially there where other sectors of law fail to achieve satisfactory results. However, causing unnatural death managed behind the scene (assassin's way) is what a lawful good character just cannot accept as a part of herself or himself and that's why assassins cannot have LG alignment.

Finished the Throne of Bhaal. I used traps to defeat Melissan. The most difficult fight was with the Fallen Solar, damn those mariliths were pain the butt. In the end i used the Staff of the Ram to take them out.

ToB was a bit boring compared to SoA but i guess it was the final chapter of the saga..