Yes--they ensure that guys living in caves are our biggest threat. If we did not have stealth fighters and stealth bombers, actual countries might think a war with the US would be a fair fight, and they might start shit.

Switzerland has a decent army, but nothing like the US. When were they attacked the last time?

Unlike Switzerland, the US is actually worth attacking. Not that Switzerland isn't, but it's in an easily defensible position. It's easy to make attacking Switzerland a bad cost-benefit. Not so much the US.

Plus we have obligations to protect foreign allies.

Yes. Americans have chosen to take on those obligations in the past.