The premises of what is accepted by many as good cycling practice is legality, predictability and conspicuity (I think Vehicular Cycling principles are based on these).

Motorists do not expect a bike to be using turn indicators. Hand signals yes. Indicators no. That addresses the predictability part.

A hand held out to indicate a left or right turn is far more noticeable than any indicator light on a bike might be. That addresses the conspicuity part.

Bikes are not required to be equipped with turn indicators. That addresses the legality part.

Now, if you have a problem in removing a hand from the bars to indicate a turn, you may need to develop some more riding skills, which in turn develop confidence. Maybe both you and the original poster need to enrol in bike skills and handling courses. Then maybe you can post derogatory comments with some authority.