Murphy's Oil Soap will remove finish - if you use hot water and a sizeable amount of soap, and a somewhat aggressive cleaning action, such as a fine brass bristle brush. However, the amount of finish removed is variable, depending on the stain/dye originally used. It contains Potassium Hydroxide (Lye) in a miniscule amount ( 2-3%). Reduced with water, the amount is but a trace. Incidentally, many commercially available soaps, detergents, etc. also use Potassium Hydroxide in higher percentages. Of these soaps and detergents, Murphy's Oil Soap is probably the least aggressive of the lot.
I have used it for years, when I feel it's necessary. No ill effects. As I mentioned when I posted the MSDS for Murphy's, there are far more damaging chemicals in tobacco smoke, approximately 4000, 70 of which are known carcinogens.
I guess if I was concerned about the chemicals in the soap, I would just use water and white vinegar to clean the pipe. As for removing stain, a drop or two of Murphy's in a cup of warm water and gentle brushing followed by a brushing with clean water won't affect the stain much. Dependent on what type of stain was originally used of course.
Aniline dyes, commonly used for staining pipes, are nothing more than fine ground particulates that can penetrate the pores and surface of the wood. They can be removed to a degree by scrubbing and hot water alone. Or let loose with the pressure washer cranked up to 3200 psi...
So with that in mind - use it - or don't...