Not sure if you are still having this issue, but I was having similar issues and after continuously running the uninstall script someone suggested running "sudo /Library/McAfee/cma/uninstall.sh" in a terminal, then running the client uninstall. So far, *fingers crossed*, it seems to have removed McAfee from my mac.
It depends on your situation. If it is indeed your computer, then the above should work.
However, from the sound of it, it wasn't put there by you in the first place; if it is a company or institution-owned machine, then removing it may be regarded as a security breach by the organization, keeping in mind that it is not "your" computer - it's just provided for your use to do your job.
As an administrator, I set my management system to clean up and then re-deploy the agent package if McAfee Security is not found in the computer's inventory scan. The alternative is that I cut off their network access, because the computer no longer meets the organization's minimum compliance requirements. Administrators don't like being undermined, particularly in relation to security matters.
You should check your employment conditions, security requirements or conduct regulations - most organizations will have a clause involving tampering with the organization's systems, including both physical (eg: security card scanner) and software (firewall, virus scanner) security systems, and indeed it may be a dismissable offence (there are certain organizations where if you change the desktop picture, you're frog-marched out the door).
You may think, it's a Mac, what could go wrong? Companies get very protective of their data, as it's often worth millions. While it might not be possible to directly be affected, they'll be peeved if an infected document is traced back to you. While you might be relatively "immune", it's about being a good citizen and not passing on an infection to others, even if it doesn't affect you.
Not trying to sound like a dick, but if it is indeed a company machine, you should think twice about messing with it, before there's a knock on your office door from someone wanting answers. Contact your company's IT group, report the fault and give them an opportunity to fix it (they can't fix things they don't know about), so that you're both happy, instead of coming up with your own unauthorized workaround.