This actually increases my desire to use Shopify, really. Not because I like Breitbart (I consider it to be drivel like most other news sites), but rather because if even they won't be booted off Shopify, it's highly unlikely that I would be. Shopify therefore looks like a very reliable and safe choice regardless of political viewpoints.
If the argument is making money off of neo nazis is about protecting free speech then you cant get upset when customers exercise their free speech to not use your product.