Bob Slate is dead--at least in Porter Square. And I'm responsible. When Staples moved into Harvard Square offering everything from padded envelopes to printer cartridges to Kindles at prices Bob Slate can't match, I complained (as did most of my neighbors) that Cambridge was becoming "Gap-ified". But no one held a gun to my head to make me shop at the Big Box store. Just as no one forced me to order books from Amazon. Or to buy a Dyson from eBay. I'm guilty as charged. And feeling ashamed that when Bob Slate closes 2 of its 3 doors in Cambridge, there will be no body to view; no funeral to attend and I'll know in my heart that I could've done more to save it.