I strongly doubt it. Mainly because many of the things we recognize and revile in today’s political discourse had a thriving existence around the turn of the century: Yellow Journalism, political machines, Anarchists around every corner… And it’s hard to argue that, say, the 70′s were a more moderated time.
It is possible that specific metaphorical frameworks and memes are more recent and promoted through a greater volume of media than back then, but there is a far greater volume of media in general.
A pro of proportional giving is that it’s dead simple to budget and keep in mind.
It can also get people to give a certain amount continually and keep them emotionally invested in charitable effort, while allowing them plenty of savings for contingencies and perhaps an eventual larger lump sum donation.
And even if it’s not optimal, “indefensible” is a pretty strong claim.