It's a slippery slope.

Meaning

Taking a particular action will inevitably lead to a series of negative consequences.

Examples

• John: 'Let's relax the regulations a little.'
• Alice: '<b>It's a slippery slope</b>; we could end up with total deregulation and chaos.'
• John: '<b>It's a slippery slope</b>; it could lead to widespread censorship and the suppression of free speech.'
• Alice: 'Let's censor this one post.'