This is the perfect example of why you don't take verses out of context and comment inaccurately about them. Let's look at more of the passage:

(Acts 18:9-11 NIV) One night the Lord spoke to Paul in a vision: "Do not be afraid; keep on speaking, do not be silent. {10} For I am with you, and no one is going to attack and harm you, because I have many people in this city." {11} So Paul stayed for a year and a half, teaching them the word of God.

When people claiming to be Christians are doing wrong we should speak up. If unbelievers are doing wrong we should speak up if what they're doing is harming someone else. I wouldn't bother telling unbelievers not to get drunk but I would tell that to a fellow Christian.