Re: Interesting justification.
"What about a jug of lukewarm/tepid water applied to the windscreen?"
Anyone doing this is the one that is the lazy one. As has already been said, two things will happen:
1. Tepid water may crack the windscreen
2. Lessening the temperature of the water to avoid the above will simply mean it will refreeze the moment you take the car out on the road.
I should know, my dad did the above when I was a kid and it did freeze up a minute up the road. This is in the south of the UK when it was cold/freezing, not in some colder climate country like in the Scandinavian region.
Like a normal person with actual sense, use de-icer.