Paypal and Ebay made it possible for me to sell things I was done with easier and for higher net prices than any other format I've ever used. Items I figured on hauling to the landfill went to make someone happy instead, and dropped money directly into my bank account. That money then was used to buy quite a few guns, including a couple of black ones - so they DO support gun rights!
Walmarts in California had numerous errors in their firearms sales records several years back. These quickly take the profit out. They don't sell firearms at any Walmart in CA that I know of. When they did, web warriors decried how they were putting LGSs out of business.
Paypal/Ebay is a business, with stockholders and such. They act in their stockholders interests. Their services are customer-controlled, but if someone uses their services to buy or sell restricted items in violation of state or federal law, several state AGs have expressed a willingness to bring suits to stop such practices. If there was money to be made, Ebay/Paypal would make it - but their risk-analysis folks say no.
Many supporters of the 2nd still conduct business with Ebay, Paypal, BofA, Walmart, and a host of others. If your kid needed brain surgery, would you disqualify a world-class brain surgeon because he was an anti?