I think of it as a health care supplement. Not full coverage.
If you knew someone who needs a $200 a month Rx that’s not on your Medicare Advantage’s covered list you’d really get this point.
It helps. It’s better than nothing. But it’s not a panacea.
I’m really lucky because my former company still paid for most of my medical supplemental (including dental and vision) after I retired. I pay a smidge over $100/mo. for all three. Also, I’m with Kaiser who has their own in-house pharmacy, so I don’t need Part D, and my monthly prescriptions (3) are maybe $15. I pay for Medicare, of course, but it’s also nominal (again, about $100/mo.). I feel very, VERY lucky.
For myself 65 is a lifetime away so I don’t worry about it and we’re happy with our current insurance. I guess some people are in constant fear of their health insurance but for us it’s never been an issue. The worst was when my wife was unemployed and I was self employed right before our first child was born but we bought a gold plan off of the exchange at the start off the year and the insurance was so good I also had a shoulder replaced. That was the closest we’ve come to making a major life decision based on insurance, we’d met our deductible for the year so we accelerated my replacement to take advantage of the cost of having a baby.
My parents on the other hand tried to cram in a bunch of surgeries and health care stuff in the years before they turned 65 because their insurance would get so much worse. I think my mom had a surgery a year from 60-64. Mostly stuff that could be done now or later like cleaning up the arthritis in her ankle so in my parents case it was a count down to more expensive and worse insurance so they did it but it was pure fear.
We are a few years from Medicare, now buying private insurance on ACA exchange. But we don’t qualify for any subsidy under ACA. So sure Medicare, if it’s same in a few years, will cover more (not everything) for less. Because, our healthcare costs will then be subsidized by other taxpayers more than they are now. Everyone would prefer to pay less for everything. But somebody has pay more than things really cost if somebody else pays less than they really cost. This isn’t ‘right wing propaganda’, it’s arithmetic.
The central issue is cost. And Medicare up to now is not particularly a beacon on how to control costs. A wholly public system could force lower costs, that to me is the central issue in general public policy debate. But that’s a huge mountain to climb after you switch to a more wholly public system, if so. Right now it’s not as if the ~1/2 public part of the US system is so obviously more cost efficient than the ~1/2 private part. If anything it’s the other way around, especially considering how cost controls on the public side seep through to cost shifting onto the private side which make the private side look more expensive than it actually is.
But yeah personally I’m in line with general older Americans’ view that ‘I paid my FICA tax’ (though that went to support Medicare and SS to older recipients back then, it didn’t go into a ‘lock box’) so ‘hands off my Medicare’ and looking forward to it, besides which, get off my lawn! 
As to expanding the program into an easy no pain solution to the US healthcare mess I’m a lot more skeptical.
Let’s be reasonable here- I clicked your second link and from there clicked this. $480/month for Part B applies to individuals with a modified adjusted gross income over $500K or a couple filing a joint return with a MAGI over $750K or married filing separately over $415K. That’s an extremely small number of people- most people are not even going to exceed $170K MAGI on a joint return and therefore most people are going to pay the $135.50.
As for me, I’m not particularly looking forward to Medicare. I will still be covered by my employer’s health insurance, which covers more than Medicare, and since Medicare will be primary, my employer’s plan will reimburse me for my Medicare part B premium, include the income related adjustment.
I said that " For Medicare beneficiaries with incomes below $85K/single or $170K/couple, the Part B premium cost for 2019 will average $135.50 per month. For Medicare beneficiaries with higher incomes, the Part B premium cost will range from $189.60 to $460.50 per month, based on income level. "