Without patents, secrecy would be the norm. Instead of revealing drug formulas, companies would lock them up forever and sue people who stole them. Patents serve a purpose, even if they are terribly broken right now.
Nowadays, finding out the composition of chemicals and drugs is routine, even if it's not simple. Reverse-engineering widgets isn't much of a problem. Disassembling computer programs is trivial.
If this is your reason to keep patents, it's not a very good one.
The argument is essentially "new medicines are good for society but expensive to develop, drug companies will only spend the money to develop new drugs if they can make a lot of money on the successes, drug companies won't make money if other people can copy the successes."
If you remove patents, we'll have some other law to give drug companies their profits. Probably something along the lines of the DMCA, which effectively strengthened copyright to deal with technological developments, but was a huge step backwards in terms of what interested parties could do with copyrighted material.
It also isn't like engineers or scientists would read patents to see which things have been invented. From knowledge implying higher damages to pure lack of readability, there are many reasons.
Secrecy without patents is fine. I find it hard to believe that any invention will not be re-invented within 20 years, even if there is no cross-contamination of ideas or any reverse engineering.