It's a slippery slope.

Meaning

Taking this action could lead to a series of increasingly negative consequences.

Examples

• John: Maybe we should relax the rules a little.
• Alice: I'm hesitant. <b>It's a slippery slope</b>; one small change could lead to chaos.
• John: But it would make things easier.
• Alice: But the long-term consequences are far more serious. Remember, <b>it's a slippery slope</b>.