slippery slope
The claim that one step forces a worse end.
A slippery slope says that if you allow one step, a worse end must follow. The phrase is standard. The argument is weak unless you show the steps. Do not use it as a substitute for the chain.
Examples
UseIf we waive the fee, we will have to waive the next one, then the late charge.
AvoidIf we waive the fee, it is a slippery slope.