For example mention how much power an always on computer is drawing and say that videos use CPU which ramps up the wattage and usage. Bright monitors use more energy than dim ones etc. Sleep mode vs always on.
If you want to go even further you could mention the carbon footprint of youtube and internet servers but this is pushing it a bit.
Of course, many people use browsers that can't handle it. That would make it literally unusable.
At 25% screen brightness, it uses around 4 Watt.
At 50%, around 6 Watt.
At 100%, around 11 Watt.
The person in question is unlikely to have a modern computer, but letting a video play all the time could technically still be using less power than the light.
A 1440p video is played at 4.0-4.5 Watt at 0% internal screen brightness.
The same video at 4k uses 4.5-5.0 Watt.
And at 8k, it's 15-17 Watt.
The xkcd is apt, as usual. The last time I felt with Intel as I feel with Apple since the M1 was with Haswell.
communicating your true feelings and intentions is the only way to grow trust. what you are describing is needlessly eroding trust.