Anti- is primarily used as the prefix to another word. For example, an antidote is a medicine given to work AGAINST a poison. "Against" is usually the more appropriate word unless you are creating a combined form. Some examples: 1. I have always argued against capital punishment. 2. I have always been opposed to capital punishment. 3. I have always been anti-capital punishment. These all mean the same thing. Number 3 is acceptable in speech, but I would not consider it good written English.

Not big difference both means -ve but against is more aggressive form it afirms ex the boy is anti civilization , it means he isn't civilised or can't coop with it but ex 2 the boy is against civilization it means that he doesn't agree or harshly disapprove it