We have been for years.
And PayPal fees are no different than merchant account fees if you take credit cards online or in a B&M. In fact, if you do reasonable volume, the discounted rates from PP are quite competitive.
eBay's fees are a business expense. We consider it an advertising expense (literally). Unlike many forms of advertising (print, radio, etc), we can actually see a direct sales result from the dollars spent on eBay. The more we spend listing on eBay, the more we sell.
Of course, your business model has to be well thought out to make a profit on eBay.
Though many try to make a killing off widgets selling for under $5 or with VERY slim profit margins, it is pretty tough—and you'll work your butt off chasing pennies and nickles. Economies of scale are much better for higher priced items