I think you're falsely assuming something here. Religious whack-job-ism is always a double edged sword. It's never a safe defense for rational thought because it's proponents will see it as a threat to them (it is) and will attack you while cheerfully ignoring anything you might bring up in your defense. Generally what makes them whack-jobs is their ability to treat anyone who doesn't share their beliefs and practices as inhuman.

You have a couple different types of appeal you can make. They target different areas and you'll have to choose the best appeal for each boss.

1. Vanity - They're the boss. In theory they have access the most important data. They're also your most important customers and it might be a good thing to point out how uncomfortable you are with providing better service to underlings than you're able to give to the boss.

2. Safety - Much like car wrecks, computer security problems don't just happen to people who are careless, they also happen to people who get caught up in the wreck. Basically just a reminder that malware and zero day vulnerabilities can nail them even if they don't do anything wrong.

3. Convenience - When was their last backup? Outline what they can expect if their hard drive bombs.

4. "Platinum Plan" - S/he's the boss. Give them a USB drive and script up a regular backup. Or do it over the network. Kind of related to the Vanity entry.

It sounds like they could filter it if they wanted to. There are a couple key points to consider here. I don't know how important any of them are from a legal point of view but I can see how they would apply.

1. They're not responsible if things look different in Chrome than they do in other browsers. Whatever causes it, you agree not to have a cow. (think acid3 test, etc)
2. If you're using their software to do google searches then it's ok if you get a safe search and not an unfiltered one (although you should be able to change this, it's just a cookie based setting).
3. It seems to cover them having parental controls in the browser. People can turn such things on by accident and not know how to disable them (or legally try to claim that the method for disabling them is deliberately obfuscated).

Realistically I doubt they'd do anything stupid like active network filtering. That just isn't what people expect out of their browsers.