We can grow crops less expensively because molecular manufacturing technology is inherently low cost.
The laws of physics should allow us to arrange things molecule by molecule and even atom by atom, and at some point it was inevitable that we would develop a technology that would let us do this.
If you think the technology is infeasible, you don't worry about what it might do and what its potential is.
If you look at the various strategies available for dealing with a new technology, sticking your head in the sand is not the most plausible strategy.
If we attempt to block the development of new technology, we effectively have ensured that the most responsible parties will not develop them.
A molecular manufacturing technology will let us build molecular surgical tools, and those tools will, for the first time, let us directly address the problems at the very root level.