The difference is that those already exist. I think concern about the development of new technology is valid.

Suppose nuclear weapons did not exist and someone was concerned about the Manhattan project — would you say that chairs enable people to build regular bombs, so we shouldn't worry about nuclear bombs?

Nuclear bombs have very few uses other than blowing up cities or threatening to do so. DNA synthesis is both of considerable use outside of bioweapons production and not really a critical bottleneck in bioweapons, which is why I'd consider it more like laptops or chairs than like, say ICBM guidance systems or weapons grade enrichment programs.

The technology already exist. The OP stated, patents are over, and that is why (s)he is working on it. Even if it not exist, security by obscurity is no security... if anybody can do the tech, the bad guys are going to be as fast, or faster than the good guys... So I hope the good guys do the tech for everybody...

You are severely underplaying how chaotic people can be, and how valuable a barrier to entry is at deterring that chaos from causing damage.