I'm actually glad that DSM-IV doesn't try to be The Scripture in everything, but respects its role as "a helpful guide to clinical practice". This leaves room for the clinician to try to understand the cultural, religious, lifestyle, and other personal factors the client brings in with him or her.
You don't have to try to find kinkier examples ;), S/M is plenty offending to me. But I can deal with my own repulsion if the client finds that kind of sex pleasurable, and it doesn't cause any clinical distress and isn't illegal. Therein lies the difference between consensual S/M and child molestation. No matter how strongly I feel that my way (or anything closer to what you or I would consider "normal") is the most natural and healthiest, it would be not just unethical but damaging to try to convince my client to agree with me. To me, it's comparable to trying to convert somebody to my religion or other spiritual belief (cf. missionary work). I'm not saying it's easy to let the client happily have his or her preferences and ideology instead of the "right" one. Especially since these aspects affect other areas of life. Who ever said our work would or should be easy!
I do not look forward to the possibility that some day I might have to deal with a necrophiliac who is perfectly happy with his way of achieving his sexual pleasure. I guess one of the determining issues there would be the illegalities involved.
The biggest experience in my own little life that taught me the hard way that there are many rights and many wrongs was when I immigrated from my native Finland 12 years ago. I'm still sometimes faced with conflicts between my ways, the Finnish ways, and the American ways. The experience has taught me the limits of my ability to better the world. ;)