Turntable tonearms use rear counterweights so the stylus presses with only a few grams

If you just let a raw diamond needle drop onto a plastic disc, you'd effectively be operating a lathe. Turntable tonearms must be perfectly balanced by heavy weights at the rear so that the stylus only exerts a microscopic few grams of downward force. Get the math wrong, and your expensive record instantly becomes a pile of plastic shavings.