There are smart switches that do not require a neutral. By design, they "bootleg" some neutral / return current on the ground wire. However, if they are legal and listed, they are tested to limit the bootleg current to some tiny amount that is considered safe by UL.
Generally bootlegging a neutral - using a ground wire as a neutral - is an unsafe practice:
The equipment grounding system (EGS) provides a path so that in the event of a ground fault, there is a low impedance path to complete the circuit, so that sufficient current will flow that the breaker will trip. In typical residential systems in the US wired with nonmetallic cable (Romex) and plastic boxes, the bare wires make up the bulk of the EGS.
Generally the EGS is not carrying current, not energized, even with the power on. In the event of a ground fault it will very, very briefly be energized until the fault is cleared. Faults generally create a dead short and short circuit current is very high.
If someone working on the electrical system, testing, troubleshooting, etc. assumes the EGC is safe, but it's carrying bootleg neutral current, they could receive a shock.
There can be some sharing of EGCs between circuits, retrofit EGCs not run with branch circuits, etc. In these cases even with the circuit you're working on turned off at the breaker, the EGC could carry current from another circuit. So in some of these circumstances, even things like plumbing pipes could wind up carrying some of that bootleg current. If there are multiple not-so-smart devices bootlegging neutral current, it could become more dangerous.
I think most would agree bootlegging a smart switch does not constitute a huge, immanent danger where you ought to get the children out of the house immediately until it's rectified.
But all would agree it's a code violation, and most would agree that re-writing the code to be more convenient for you, or picking and choosing where you're smarter than the code, is some dangerous hubris.
As mentioned in another answer, smart switches with remote units that can be installed at the light are a safe alternative.