An interesting one this, and one that I often think about having elected to spend three years studying sex offenders, who are surely amongst the most unpopular groups in society. There are a number of questions that need answering though and things to bear in mind. Above all, I think there are two sides to every story - and it is the job of those representing clients to find such sides. Second of all, it is our job - certainly my job, to understand what is going on in peoples lives and convey this. Whilst a lawyer may not be able to excuse, he could at least give an insight into mitigating circumstances and provide a full account of the factors on which a decision could/should/may be based upon. Lastly, I think it is important for the continuing legitimacy of and confidence in the legal system for good quality representation to be at a clients disposal. Even if one isn't able to excuse what a person may have been done, one could at least ensure that the rights that *everyone* is entitled to are upheld.
For these reasons, as well as others therefore, I would not refuse to represent a client, no matter how "unfashionable" the case.