Copyright can still exist, as well as licensing and IP law and trade secret protection. Patenting is just saying "we'll disclose this invention in exchange for a temporary monopoly".

It's especially problematic in software because algorithms are very closely tied to fundamental mathematical axoims. For example, you can't just try really hard and make a O(n) sort. There is no benefit to society to granting a monopoly on a faster O(nlogn) sort