Dhampirs are half-human, half-Moroi beings. All dhampirs have one Moroi parent and they may not even know one of their parents, depending on the family. Since dhampirs cannot reproduce with one another, it is important that the Moroi race continues to live and is protected. WIthout the Moroi vampires, the dhampirs would cease to exist, eventually.
Because of this, most dhampirs are trained to become guardians for the Moroi. They possess the best traits of both the human and Moroi species.
Dhampirs are able to go into the sun with no problem whatsoever, therefore the watch over their charge is easier.
The better a dhampir does in their trials towards becoming a guardian, the more they are likely to be able to choose who they wish to protect. Royal Moroi typically get better guardians than other Moroi and are also able to choose their guardians, granted the person in mind has graduated from one of the several Academy settings around the world and has their Promise Mark.
Dhampirs appear human, but are slightly more attractive and taller. They are also stronger, have more endurance and are infallible to most human sickness(es) because of the Moroi blood that flows through their veins.
Dhampirs do not have fangs, therefore they do not drink blood and survive on a regular human diet, though what they eat has to be healthy so they can stay in shape enough to successfully protect their charge.
Dhampir men and women that choose to not become guardians are often dishonored and looked down upon. Women that stay out of the guardian lifestyle either end up in ‘blood whore’ communes, or find a different place to live so they can start a family with a Moroi man. It is very rare that a dhampir woman finds a Moroi man willing to stick around and actually raise a family, so after the children are born, most dhampir women end up single mothers some way or another.
Since guardians are becoming increasingly harder to come by, there aren’t enough to go around. Royal Moroi are almost always with two or more guardians that they often choose themselves. Some lucky Moroi are paired with at least one dhampir to help protect them. When a male dhampir doesn’t go through with becoming a guardian, it’s seen as a great disgrace and a huge loss, because Moroi need the dhampirs as much as the dhampirs need the Moroi. Without adequate protection, Strigoi would pick off every Moroi they can get their hands on. Since Moroi are not supposed to use their magic offensively, this puts them at risk for attack when they do not have guardians.
This is why Christian and numerable other Moroi want to be able to practice and use offensive magic. Some night, there will be a Moroi out at the wrong place at the wrong time, and they won’t know how to protect themselves long enough to get help from a dhampir that can effectively dispatch the Strigoi attacking them. He genuinely believes using magic offensively would help this problem. If they can’t have a guardian, they should at least be able to help themselves instead of cowering and running for their lives.