1
general::
A dangerous course, one that leads easily to catastrophe, as in He's on a slippery slope, compromising his values to please both the bosses and the union. This metaphoric expression alludes to traversing a slick hill-side, in constant danger of falling. [Mid-1900s]
American Heritage Idioms
2
general::
Phrase(s): a slippery slope
a dangerous pathway or route to follow; a route that leads to trouble. • The matter of euthanasia is a slippery slope with both legal and moral considerations.
McGrawhill's American Idioms And Phrasal Verbs