There seems to be a great deal of confusion about Guardians as a Calling. However, it seems relatively well accepted within our community that being a Healer can be a Calling. I'd like to propose the following paradigm in which to consider the question of exactly what might define a Calling, and the various parallels between being a Called Healer and a Called Guardian.
There are Healers who believe that they are given gifts and talents for healing people, that those gifts and talents are to be channeled almost solely into healing people, and that misuse or disuse of these gifts would be devastating or detrimental to their overall health. Some Healers never give a single thought to why they do what they do, they only know that it is either unthinkable or terribly damaging not to do so.
Due to the nature of this "Punishment" for not healing, many Healers consider healing to be a supernatural obligation and believe strongly that there is absolutely no choice but for them to heal.
Some Healers actually conjecture the source of their healing obligation. Some consider it to be a choice, some believe it is by divine oath, and some believe it is by adversarial curse. For some it is a choice or obligation that bridges many lifetimes, or perhaps every incarnation of their soul, while for others it is limited to one incarnation.
It is also quite possible for someone to be both a healer and a guardian by calling. There is no rule that says that one must have only one calling at a time.
I can see Healers taking a temporary role when necessary to guardian because one of the possible tennents of being a Healer is preventing illness and injury in the first place. So someone in a terribly bad position might need preventative measures taken to avoid the need for future healing. Not all healers are willing or able to prevent things in certain situations...and not all healers are trained in normal preventative measures (nutrition, for instance).
If a healer sees a child about to get hit by a car, I would think they would sweep the child out of harms way and run like the dickens...that is a guardian role, in that moment. Some guardians have a primary call to the actual prevention of situations which are inherantly dangerous to others, thus they are helping to forefend the need for healers in the future, and some are trained enough in healing to actually bind wounds, staunch bleeding, or perform laying on of hands, etc. They are not incompatable.
Can someone be equally both? Probably, why not? There have been monks and priests in the armies of the Crusades. I don't agree with some of their ideas, but why the heck not? Healing and guarding are not incompatable. I think that people are looking at Guardians like they're some sort of ultra-violent group or something. They are healers, in their own way...and healers are guardians in their own way too. I'm not implying that one is a subgroup of the other, but there are paradigms to use that take into account the overlaps...
A guardian who closes rifts or gates is healing the fabric of space-time...they can be healers of the energetic balance in an area, or work on preventing injury in the future, and returning wayward beasties to their homes can be healing for those beasties, because it probably isn't too comfie here for them. A healer who saves a life is guarding the person's life force...they are a guardian on a personal physical/mental/emotional/spiritual level.
To say that Guardians only kill dangerous entities is kinda like saying that the job of police officers is to kill the criminals. But that's not true. They have rules and codes to go by, and are *supposed* to only use deadly force to deal with deadly situations. They deliver babies, they give CPR, they apply pressure to wounds, they ticket people who are being reckless and dangerous and might injure someone in the future if they continue being assholes. They serve many roles.
Conversely, to say healers are only healers is like saying that all ems workers do is heal, deliver babies, administer CPR, etc. Sometimes they have to break down doors to get to the patient, sometimes they have to use force in order to heal...tie the patient to the gurney, drive agressively to get to the emergency room before they die, and I imagine in some cases they get guns pointed at them, beat up, shot at, etc. when they are, for instance, taking a battered wife into the hospital and the husband is still present. If I were an ems worker, I'd surely pop the bastard in the face if he got between me and my patient. :)
I see no inherant conflict.