1) IMO, software patent should be globally banned
I disagree. However, I do believe that there are too many frivolous patents.
But consider the whole idea of why patents exist in the first place, which is to allow you to be compensated for time and money that you spend developing a process, and stop others from making money off your R & D. Without patents, almost nobody would do R & D work. This applies just as much to software as it does to anyone else. If a software company spends two years and several million dollars developing new algorithms, they should be allowed to protect that investment, otherwise anyone who can disassemble code can duplicate it at almost no cost.
Out of interest, do you have examples of patented software algorithms that took years and millions of dollars to develop?
Disassembling source code is something that is going to be a big risk for companies in many cases, even without software patents (e.g., accusations of copyright infringement).