Home Depot probably thought they didn't want their employees wearing religious pins because they might offend atheists or those of a different religion, the same as they probably wouldn't want one of their employees wearing an atheist pin because it might offend religious customers.
Some might lay claim to the issue of freedom of speech. I have two thoughts on this. The first is we do not allow the likes of Playboy in our school system, so why should we allow Home Depot's employees to feed the religion issue, regardless of his beliefs? The second is freedom of speech is only as good as how far you are willing to allow it. Do you exercise freedom of speech for yourself and not others? If so then you're the last to bring up the issue.
Even if you think everyone from pedophiles to terrorists to Sith is entitled to have their say it should be considered not only whether they should but in which context they should be allowed. A Darth Lord could say what he wants on Korriban, and while he or she may believe to be entitled to do as they please trying to force Sith philosophy on, say, Coroscant is not going to end well.