If i see a low level horde on my way somewhere, chances are I will mess with him or kill him. For one main reason:

I don't like horde.

I'm not flexing or showing off skills. I am killing you because you are horde. I do the same thing if I see a level 70. This is a video game, and I play it to kill things, not build a caring and functional society. Horde ranks up high on those things I like to kill.

There are a couple pro-ganking arguments to make though.

1. There is no reason for anyone on a pvp server to not expect to be killed. If you think there is an unspoken bond between horde and alliance that allows you to quest in harmony, then you shouldn't be on a PVP server. There is no truce. By ganking lower level characters, you assure they don't think they are playing World of Carebears.

2. Protect our lowbies! Horde in STV or tanaris or another equally contested area, i'll help out the cause and kill some horde. Although you could argue this will just anger them and make them attack lowbie alliance that they wouldn't have attacked otherwise... in fact they more than likely will do just that. Good thing or bad? Up to you, the one getting killed.

3. I'm not ganking out of revenge, but I certainly want the horde to reach level 70 with a fighting attitude looking for revenge!

I am against camping because it really isn't much fun for either party. If I initiate a fight, i will kill them and continue on my way or continue whatever I am doing.

To be honest, I much prefer ganking solo 70's over lowbies, but I'm not going to run by, smile and wave just because you are a low level.