In today's world, everyone is a software developer, it seems. Without patents, how would anyone build a company on a good software idea. The examples given (online shopping carts, credit card processing, etc) may seem silly now, but imagine the first one. Today, if you launch a good idea, it would not last a month before another group of developers had taken your idea and created an "inproved" version. The only retribution would be that their version would also not last a month. This is the reason for patents. Maybe there are some aribitrary grants out there, but it is the idea that must protected, not just the specific code. It is too easy to write different code that steals another person's idea.
If we think competition is ugly now, just imagine a world without patents. Huge software companies can rest on them now and try to gain the advantage through the protection of the patent. Without that protection, the methods for obtaining a strong foothold on the market with any "new" ideas could only get worse.