[SixOfSpades]

Originally posted by Cerek: 1) .... is there a way a Neutral Good character can justify breaking into a mage's house and killing him based solely on the behest of another character that the PC knows is evil?

Breaking into a Cowled Wizard's house--yes, a NG PC might see this as an idea opportunity to say, "I've slain your pathetic Mephits, I've deactivated your hapless constructs, and just what do you think I might do to you if you don't tell me how I can find out where Imoen is?!? Start talking and I'll pay for the damage I've done. Refuse to speak and suffer the consequences."
Actually killing the Cowled Wizard, at least without any additional reason to do so--I don't think so, no.

2) The execution of Viconia. Could a Lawful Good or Lawful Neutral PC justify intervening in an execution which - as far as they know - is being conducted in accordance to the Law? Since both alignments put a heavy emphasis on obeying Law (even if the individual disagrees with a particular law), is there anyway to justify them preventing an execution that may be perfectly legal under Athkala's Law?

The whole "appearance" of how official the execution is is rather iffy: True, there are guards there, but the fact that the execution is being emceed by a Priest of Beshaba indicates that something isn't quite right. Now, the city of Athkatla may have authorized the church of Beshaba to conduct executions without a civil official present (the city does have a large, fancy Temple of Talos, after all), or it might be a simple mob. The fact that the leaders are called "Fanatic" might mean something, the fact that Viconia claims to not deserve death does not. What I find most interesting is that Viconia does not claim to have been denied a fair trial--such a thing would be alien to her native culture, but she's been aboveground long enough to know how most Human nations do it....and she makes no mention of being tried at all. Does this mean that she DID get a trial, and if so, was it a real trial (such as the one that Saerk Fahrrad allegedly gets), or simply a sham 'mob' trial, which was enough to fool a Drow who wouldn't know the difference?

In short, I don't think the PC could know enough about the circumstances of the event to make a cut-&-dried decision, not at least before the Flamestrike hits. If there is any clear indication of the scenario, it is, as Q'alooaith said, the fact that the Fanatic questions whether Viconia's Drow ancestry is not reason enough for the killing. How a Lawful character would interpret this, I don't know--Athkatla may very well have a perfectly legal set of edicts against Drow, especially vagrant Drow, within the city.

3) What about the "fee" required by the Cowled Wizards to allow the party members to cast spells? Can a lawful PC justify NOT paying that fee in order to save their gold? Can they justify killing the Cowled Wizards when they attack the party for violating the rule and casting magic in public without a "license"?

Here it is different: In the case of Viconia's execution, the PC suffers from a lack of information. With the Cowled Wizards, however, we see that although they claim to grant licences only to "fair and careful practitioners of magic," they do in fact give a free hand to anyone who pays the fee. So what if a Githyanki war party fries a few Commoners with Lightning Bolts? So what if a Mad Priest of Cyric calls down Horrid Wiltings at random? So what if there's a Lich chasing you around the City Gates District? As long as the Cowls have their money, they could give a damn.
Ordinarily, a Lawful character would either pay the licence fee, or simply not cast Wizard spells outdoors. If he knew what I know about the Cowled Wizards, however, he would see that it's they who are not behaving in a Lawful manner. The Cowled agenda isn't safety and stability--it's lies and extortion. Death to 'em, and set up someone responsible in their place.