I think that it's a communist plot!
I think this bad idea is something cooked up by the nursery industry in order to sell more plants & avoid having named cultivars reproduced.
Named cultivars cannot be grown from seed. The seeds will grow into very nice flowers, but the plants will be different from the named cultivar.
In my garden, I've done side by side testing of whether there actually is a difference of more flowers with deadheading. I found that my perennial flowers did better when they were allowed to set seed. I found that allowing the plants to set seed resulted in more birds being attracted to my garden. I also found that my garden was more visually appealing with the seed pods adding multiseasonal interest.
Of course, as with anything, your results may vary. Just don't mutilate your plants and expect compliments from me.