I'm sure you've heard them before, but try:
- Leaving would mean business must still comply with EU laws but we would have no say in setting them
- Being in the EU gives Britain access to a huge market for our exports, bringing jobs and prosperity
- Being in the EU allows Britons to work there, retire there, and get free healthcare if they fall ill on holiday
- Being in the EU attracts investment - global companies are based here because we are part of it
However, since you've already made up your mind, it is a waste of time saying anything to you.