two points i would like to make because i see the political understanding of some people in this thread is truly regrettable:
1. bernie sanders is not "far left" in any context in any meaningful sense. when i think far left, i think radicalism, in other words a rejection of the liberal* political (and economic) status quo as it currently exists for typically socialist, feminist, anti-racist, anti-imperialist reasons (some leftists are only some of these things but i find that such an anti-intersectional approach is not terribly conducive to "leftism" as a whole). bernie sanders does not reject the liberal political status quo, he merely seeks to work within it to reform certain things in order to reduce social inequality, so we might call him a "left liberal" or something along those lines. if your definition of "far left" is just some vague notion of being to the left of a perceived political center within a given context, i do not see how an accusation against someone of being "far left" is a meaningful critique in any way
*when i say "liberal" i mean this in a meaningful sense, not in the way americans typically deploy it. if this confuses you, study the philosophical tenets of liberalism
here, for example
2. building off my previous point, this divide between "the left" proper and progressive liberals or what have you also serves to explain why a group of people here do not find voting particularly important while others think it is The Most Important Thing Ever. if you are a liberal, you obviously find voting important because voting is, according to the political system you support, the primary way of acting politically. the goal of a progressive liberal is to reduce harm by voting for a government that gives more to social programs, socializes health care, strengthens gay rights, et cetera. however, if you are a leftist, you believe that the issues that cause social inequalities are necessary components of the existing political and economic order and that any progressive reforms will not hold in the long term and will merely temporarily alleviate inequalities. you do not have to have a degree in political science - although i do - to understand that institutional problems cannot be truly resolved without completely reworking if not abolishing said institutions. reducing harm by voting for the guy who's more "to the left" than the other guy therefore is simply not nearly as relevant to a leftist's politics compared to those of a liberal. this does not mean that a principled leftist has no reason to vote at all, just that there are less good reasons to do so and more reasons not to
as an aside, i expect some people to question how it is possible that, if bernie sanders is not actually far left, a number of vocal bernie supporters argue against voting biden. to this i would simply reply that when one grows up in a liberal political culture, one learns to talk and think like a liberal. some fledgling leftists accept a lot of radical left arguments (such as the fact that institutional problems require institutional solutions) but are not yet principled in their political position and hold on to certain tenets of liberalism, since that is what they grew up with (and one does not go from liberal to marxist overnight, believe it or not). other anti-biden bernie supporters may actually just be progressive liberals at the end of the day and have simply adopted something moreso resembling a radical position wrt voting in a positive moment of confusion - i suppose these are in some sense "bad liberals" and maybe in their case your "voting is your Duty" arguments may hold some water