In General
Most areas within the Game have only a very small number of NPCs. Most of these are pretty low-level and so are easy to kill. This may make them seem an easy target if you feel like 'being Evil'.
However, most areas, especially the major cities, have a population far larger than these few NPCs . Also, many of these people are experienced fighters or powerful mages - not just level 1 Commoners. Therefore, it does not make sense IC for one or two PCs to go on a rampage in a City and kill every NPC they find. This would represent those one or two people killing hundreds, if not thousands, of people. You are not Chuck Norris or Stephen Seagal. Your PC is not capable of killing this many people without a scratch.
The correct way to do this is to ask for a DM to watch over your attack. The DM will then sound the alarm, attracting all PCs on the server to the area of the attack. He or she will also summon a large number of guards, who will probably be beefed up enough to allow your PC an opportunity to visit your Deity at least once.

This may not be the result you hoped for, but is much more realistic and in character.
Cities
You sneak up to the City and start your attack. You might attack the gates openly, or you might wait until you have reached the inner areas before your attack - more like a Terrorist attack. If you do not have a DM watching, then you kill every NPC around, gain about 1 or 2 XP each and we get annoyed afterwards.
If you have DM supervision, you get a much more realistic result. If you are strong enough, then you might get some reasonable XP and maybe even a cookie or two from the DM. If not, then maybe your God will give you tips on better tactics.
Temples
These are not as poorly defended as they might appear. Although you only see one Priest or Priestess, this is a Holy Place - the Gods get upset if their personal temple is desecrated. The Gods are powerful and will pwn you if you upset them.
Seriously, a Temple must not be attacked without DM approval and supervision. No exceptions, please don't do it.
Outlying Farms and Villages
These will still have a lot more people than you actually see. Since the War only ended recently, you can safely assume that most of these know how to use a weapon. Although a successful attack on these is much more likely, even these should not be as easy as they might seem. The occasional assault on a small farm might be acceptable, although it is still worth just mentioning this to a DM first - in case he or she wishes to spice it up a little for you.
Conclusion
If you just want to play at being Evil and kill a few easy NPCs, then perhaps you have the wrong impression of playing an Evil PC. If you prefer a realistic challenge, then a friendly note to your local DM will prove much more satisfying an event for you.

In WoW, all Cities and Towns are guarded by Elite NPCs of the opposite faction to your PC. Thus, you might be able to make an assault on one of these if you are strong enough, but it will not be easy. Killing Commoners gains you no XP. In Avlis, we do not have that facility, as there are far more than just two factions. So here, you need a DM to assist you.
Unless you prefer to be pwned by us of course

Consequences
A breach of these Rules will result in an OOC consequence for you and probably IC consequences for your PC. Remember, the actions of your PC will annoy a lot of powerful people in Game. However, it is also Breaking the Rules, which will be dealt with OOC. It might get your whole character list jailed for a while (meaning you cannot play on Avlis), or repeat offences might even get you Banned permanently.
Do not do this.
*This is an update and replaces previous Rulings on AI Abuse*