"Already" at the beginning of a sentence

This sounds like a personal preference rather than anything to do with the way English is actually used. It was good enough for such talented writers as Robert Louis Stevenson:

Already in our society . . . the bourgeois is too much cottoned about for any zest in living.

and Betrand Russell:

Already in December 1676 Leibniz held that not all possibles exist.

I don't see a problem with it. I suppose your friend would say that the sentence should be written, "People were already watching television in their homes in 1930." But we often vary word order for emphasis. I don't see how putting "already" at the beginning creates any ambiguity.

In some ways this resembles a dangling modifier. Like, "Showing signs of drunkenness, the bartender refused to serve Fred." It's amusing because the structure of the sentence indicates that it is the bartender who was drunk rather than Fred. You need to be careful about re-arranging a sentence in ways that create such an ambiguity or flatly incorrect association.

But in your example, I don't see a problem.