The concept of deviance is value laden by definition: it means, by its dictionary definition, behaviours that go against cultural norms. These include officially enforced norms (and thus crime is by definition a deviant behaviour, at least in societies whose legal rules have social legitimacy) or unofficial social norms, from etiquette to norms of “decent behaviour” to standards typical of particular class or in-group. As social norms vary from society to society and from historical period to historical period, it's clear that deviancy is a cultural construct as much as social norms that it deviates from.
The semantic shift from “deviancy” meaning “deviant behaviour” to “deviant perspectives” is even more (if possible) value laden. As much as most people accept that societies need a system of norm to regulate interaction between their members, a lot of modern western political and social philosophy places very high value of the freedom of thought. It's pretty universally accepted that we should refrain from most seriously deviant behaviours, but imploring people to refrain from deviant thinking, deviant ideas and deviant perspectives has a whiff of Holy Inquisition about it.
Still, we can treat “deviant perspective” as a purely sociological term and simply assume that every unorthodox, unusual, non-standard or rare perspective/system of attitudes and beliefs is to be considered deviant. This is, obviously, an entirely relative term and what is a deviant perspective in one time and place is a standard, received wisdom in another set of circumstances.
Belief in a god used to be a standard perspective in all European countries for thousands of years, but it is becoming borderline deviant in some heavily secularised societies, for example Czech Republic, Sweden or France. Belief in inferiority of non-white peoples was rare in medieval Europe, extremely common among the 19th century Europeans whose prosperity as being built on colonialism and since then became less and less acceptable, to have now a deviant (and in some countries, criminal) status.
There is also variation within larger societies: in Europe and most large American cities theory of evolution is a standard perspective that most people pretty automatically adopt when thinking about the natural world, and creationism is considered deviant, but in regions of American Mid-West the situation is opposite.
For all those reasons, there are many paths that lead people to convert to deviant, non-standard or non-traditional perspectives.
(1) The first and probably most interesting reason for conversion to deviant perspectives is being, to use a marketing term, an early adopter. Some people are sensitive to the Zeitgeist and will convert to the new way of seeing things simply because they tend to “go with the flow”, others are genuinely attracted to the new ideas. Such conversions usually precede a paradigm shift (this term is used here very loosely and not particularly for scientific paradigms) after which the old deviant perspective becomes the standard one.
(2) Some people – because of their temperaments or because they are in a phase of life or circumstances that prompt that – are attracted to deviant perspectives precisely because they are deviant. The conversion fulfils their need to be different, to rebel, and to contest the status quo while at the same time belonging to a group of their own. In such cases the particular characteristics of the deviant perspective are not very important (this is the case with many youth and underworld sub-cultures).
(3) Some people convert to deviant perspective that appeals to their natural preferences or allows them to fulfil particular needs that are unfulfilled under the mainstream set of ideas. A good example is asexual people or those with very low libido who join religious orders (in which their lack of interest in sex is an advantage rather than a subject of inquiry and derision).
(4) Some conversions are purely utilitarian: people take on a new set of attitudes and ideas, often at odds with what's socially acceptable, because it's advantageous and convenient for them, either for material or status reasons. Joining a right-wing party that is likely to win the election in order to gain personal power is a good example of such behaviour.
(5) And finally, some conversions are better understood as symptoms, or expressions of real mental illness. Conspiracy theories are a typical example of deviant perspective that appeals to individuals who already tend to have either paranoid personalities or sometimes suffer from real, full-blown psychosis.