START is meant to decrease the ability for nations to use offensive missile technology to destroy one another, so of course it does not preserve the capacity to use such technology. It would not be able to work if it did not neuter the ability to use such technology in the first place.
New START does preserve missile defense capabilities. The treaty reduces constraints on missile production and does not put a limit on how many missiles the U.S. can build. While some news outlets have stated otherwise, U.S. national security experts are behind the New Start Treaty. Our missile defense capabilities remain in tact.