A Question Relating to Dogs and Islam

From what I can see by doing internet searches, there seems to be a number of different interpretations and contradictions regarding dogs and Islam.
It appears that in some stories, the Prophet prayed while dogs were playing around him. I have also seen how different traditions in Islam appear to hold alternate views on dogs - while some consider dogs to be unclean, others consider the saliva, but not the hair to be impure. I have also read that the Sunni Maliki school considers dogs to be pure.

I also find it very interesting - and this related to my original post - that some dogs - such as the saluki, sloughi and similar, appear to have traditionally held an elevated status as compared to others. Many articles indicate that these hunting dogs were allowed into the home. Furthermore, amongst Arab peoples, the Saluki is referrred to as "al-Hurr" or "El Hor", the "noble one", rather than "kelb", the word for other dogs.
http://www.saudiaramcoworld.com/issue/197302/al-hurr.the.noble.one.htm
http://www.tandfonline.com/doi/abs/10.1080/714041375

What makes these dogs so different? I would guess that a key historical differentiation may be between that of a prized hunting hound and a feral street dog. It has been suggested that the designation of dogs as unclean may originate in the prevalence of rabies in the region during the time of the Prophet. Also, it would be fair to surmise that the flea, tick and worming treatments that we use today, were not - and still are not, in many parts of the world - available. There is a problem with this theory though...

Much has been made on this thread of the supposed unhygenic nature of dogs with regard to disease, certain habits etc. However, cats appear to be acceptable in Islam, yet cats may carry just as many of the diseases that dogs are supposed to. Cats can have rabies (in countries where the disease occurs), while toxoplasmosis may be caused by cat faeces. Of course, as with the canine equivalent, occurences of this are extremely rare. Like dogs, cats also lick their own behinds. Both animals then, can be seen to have some unseemly habits and can carry zoonotic diseases, yet why are cats accepted? I would love to know, particularly in light of the implication here that people who live with dogs will all die a horrible death as a result.

There are other theories as to where the problem with dogs came from. Some indicated that the issue was picked up on as some pre-Islamic cultures took issue with dogs - particularly black dogs, a superstition that was also common in Europe. As we are all aware, religions have historically sought to incorporate some elements of existing traditions in order to successfully convert the masses (our own St Brigid for example, is also a goddess in pre-Christian traditions). Conversely, it it suggested elswhere (Mary Boyce, 1979, "Zoroastrians, Their Religious Beliefs and Practices", p. 252), that early Islam was not particularly averse to dogs, but that the hostility to them was fostered with the Islamic conquest of Persia (Iran), as part of the subugation of the indigenous Zoroastrians who considered dogs to be sacred.

Whatever the origins and interpretations, it helps nobody to try and use pseudo-scientific ideas and random Youtube videos to try and cast dogs as unclean. As has been said by other posters, if dogs were so diseased, then all of us who have kept them for many years, would be horribly ill. Indeed, many studies show that children who grow up with pets have stronger immune systems and are less likely to suffer allergies than those who do not. Furthermore, dog ownership has been proven, in numerous studies, to have many health benefits
http://www.rte.ie/worldanimalweek/benefits/index.html

Finally, I think it should stand to reason that the interpretations of what dogs are permissible or not, or where they should be kept, could be adapted to modern society. After all, living conditions in the time and place of the Prophet are vastly different now. For example, pet dogs today may also be said to provide a guarding duty, by alerting their owners to anyone approaching. In some circumstances, particularly in city houses or apartments, this duty is best performed by the dog being in the house. Similarly, given the aforementioned health benefits of dog ownership, surely these give the dog a "purpose" compatible with Islam?