"The truth about the LED is that if powered by a regulated source at the manufacturers voltage specification [...] "
Perhaps you've missed Amanda's explanation that there IS no set voltage; it varies, not only per batch but also by temperature. And that current varies a lot as supply voltage varies a little.
"It is true that if the voltage is steady the current is steady.". Yep. But it's a big 'if'. If temperature of the environment varies, Vf varies a little and If will vary a lot more. As the LED heats up its Vf and thus If (in a voltage source) will vary. In a current source, If will stay the same no matter the temperature, Vf of the LED, etc.
There's little doubt in my mind why others, with more electronics knowledge than I have (unlike you, I'm just self-educated on the topic) don't bother to answer you. Your statement is so wrong as to be looking like a troll post.
In fact, the way you behave in here (when newbies start throwing tantrums, I immediately assign the 'troll' label to them; call me a bigot), I think you are.
By all means, power your LEDs by a voltage source. But if you start exhibiting incorrect information in here, expect to be criticized. 'Truth' is written with a capital 'T' in here.
'Why not design a PWM circuit [...]'
I'd say, put your money where your mouth is. Amanda has given us some simple circuits; why don't you give us a much better one, a PWM driver for the LEDs?