The big objection that I have heard is that shaving creme is acid and will eat the stone away. If you read the label, you will note that it does contain stearic acid. The true acidity of any substance can be determined by measuring the H ion concentration in the substance. This is also known as pH. The pH scale ranges from 0 to 14, with 7.0 being neutral, less than 7.0 is acid, and more than 7.0 is basic. The cases that I am aware of, shaving creme ranged between 7.0 and 7.5 in pH. This says that there are no free H ions to react as an acid in shaving creme.
Stearic acid is a long chain fatty acid.
It is quite common in beef fat, but is in the triglyceride form. There are 18 carbons in the chain making up the acid. Rinse the stone off with water. The main reason that I rinse the stone is for esthetic reasons. People will feel better about it.