That's not what Paul is saying. Paul is saying that just because somethign is permissible, that doesn't mean it's adviseable. No one who says the consumption of alcohol is always adviseable (such as, consuming alcohol in front of a drunkard). It is, however, permissible, and if it is permissible, then we must permit it. For example, there is absolutely nothing scripturally wrong with a Christian being out at dinner, and having a glass of wine with dinner. That's a reasonable way to consume it, and it is neither a stumbling block nor a bad witness to any resonable person, Christian or not.