I'll go at these a little out of order, so pray excuse me, but it makes organizing my thoughts a little easier.

From my limited understanding of node XP, it does not make sense for a user to have the ability to, as you suggest, '"lock" it's [sic] node, thus making it's current XP unchangeable'-the whole point of a node's value is supposed to be how useful or not someone finds that node. As to the facility to force a message (/msg) from the downvoter to the downvotee, truly they should comment why they are doing so anyway, either in private via /msg or in public by a posting in response to the node.

I disagree somewhat with your title premise. In the context of the Monastery, definitions 1 and 3 of the third entry for the word sin at dictionary.com seem the most appropriate (to wit, a transgression of moral/religious law, especially if deliberate, or something shameful/deplorable/utterly wrong). I'll grant that personality voting is perhaps immature and should be avoided, but then again, I consider this over-fascination with XP and the extremes to which people try to preserve it to be slightly immature as well. I would reserve the term "sin" to be more like doing something that is a known wrong, such as intentionally writing insecure scripts or such without just cause.

<soapbox>At the moment, I have been here for about 1yr 4mo. In that time, I have seen numerous postings about people whining and complaining about the XP system. I have, sadly, even stooped to responding before. XP is like bogomips-a made-up value, which should only be used as a relative indicator of how appropriate and useful that particular contribution is, and if it is low or negative, maybe you should look at how your suggestions compared to that of others on that topic, and see if there is a way to improve yourself or the way you presented yourself for the next time. Point is, you can't legislate or force people to be mature-they must learn to do that on their own, and personality voting many times may show that lack. So, as the Eagles song goes, "Get over it."</soapbox>