I first heard this argument in Reagan's day. It's getting a bit old.
First, 90% of Americans do not live in a swing state. Their votes for President are mathematically worthless (I can say that as a mathematician). If you're one of this majority, you can vote as you please.
The second part of this argument is that it's always used after the DNC have nominated some wildly unpopular candidate that they are terrified will not win. It would be better if instead of the DNC stepping in to grossly interfere with their own primaries, unilaterally changing their own rules for no apparent reason, they tried to select a candidate who might actually be popular.
The US has steadily lost ground for over 40 years. Each candidate is to the right of the previous one - each candidate, whether R or D, supports the endless foreign wars, supports unchecked Wall Street lawbreaking (Wall Street firms pled guilty to thousands of felonies under Obama, and yet no one spent a day in jail), supports fossil fuels.
Each time, we are presented with a more right-wing Democrat than the previous. Each time, we are mocked for not wanting to support this candidate who really shares nothing in common with us.
Each time progressives trudge out and vote for the candidate they hate anyway. Did you know that almost twice as many Bernie supporters voted for Hillary in 2016 than Hillary supporters voted for Obama in 2008?
Progressives always vote in great numbers - they are consistently the second highest demographic to vote Democrat, after seniors (who are always the top for both R and D).
The people who do not show up are poor people, people of color, people with no hope - because they quite rationally believe that there will be no change at all in their condition no matter who wins.
But at the end, if the Democratic candidate loses, we can be absolutely sure that there will be no self-examination by the DNC. They will simply mock and revile the progressives, dust their hands off, and call it a day.