A large number of serious scientific and economic studies justify ruling out patents on software.
Software authors are already protected by copyright law, allowing others to innovate in the same space generating healthy competition, but this protection is undermined by patents on software. It is far too easy to violate patents on software whilst being completely unaware of any transgression. Software companies do not use and do not need the patent system to innovate. They must be protected from owners of dubious granted patents.
Software patents miss their legitimate purpose. Patents on software favour litigation in detriment of innovation, defeating their democratic justification. They force software producers to spend on bureaucracy, lawsuits, and circumventing dubious granted claims on software what would otherwise be spent on Research and Development. Owners of patents on software, who sometimes doesn't produce software themselves, obtain a means to exert unfair control over the market.
In the USA there are billions of dollars in litigation over software patents each year, and not only between software companies, but also other companies just because they have a web site (this starts to happen in Europe also). This mistake needs to be avoided in Europe.