Using a Turing-complete language does not mean that all possible programs written in that language are undecidable. As a trivial example, if a particular program doesn't have loops or recursion, or if it loops for a fixed number of times, it quite obviously will halt. More generally, it's possible to write simple code with clear and obvious effects.

If were really that bad to use Turing-complete code, then smart contracts would be the least of our problems, because Turing-complete code runs our airplanes, medical equipment, and nuclear reactors.