Software patents are pretty close to universally bad. Software moves fast and twenty years is ridiculous, when video codecs have grown to be biggest format and then been overtaken by their successors which in turn are overtaken by their own successors before the first codecs lose their patent then you know something is going wrong. Hardware patents have their place as you say, but software moves very quickly and can innovate just fine without the need for patents.

In theory you could make them viable by shortening the life, to just 5 years or something, but at that point the cost of administering them probably outweighs any benefits (if there would actually be any).

Copyright is another matter, I think we probably need that in some form (though the stupid length of copyright at the moment is even stupider for software)