The phrase "slippery slope" means that if you take one small step in a certain direction, it could lead to more and more serious consequences that are hard to stop or reverse. Full definition
Certainly, this is a local issue and I am concerned, like many of you who are voting no, about the proverbial slippery slope of what will happen next. (politico.com)
On this topic, the negative pull on the believing boyfriend or girlfriend down slippery slopes is typically what gets highlighted in the argument against dating outside the faith. (relevantmagazine.com)
They saw it as a dangerous, slippery slope toward changing all other rules, including the 21 million coin limit. (links2exchange.net)