People run against Putin as well, he just defeats them all.
The bottom line, if you vote for someone that means you find them acceptable and fit. Voting is ultimately an affirmative action.
Voting for someone who wont "win" has great merit when none of the "leading" contenders will result in any net benefit.
The problem with your "lesser of two evils" approach:
You are probably familiar with Darwin's various theories. Heres the thing - selection happens on a societal level, not just a biological one. If you affirm garbage politicians, you are affirming a garbage society. When the "lesser of two evils" is still evil, meaning, in this case, a net negative societal impact, then affirming such with a vote is nothing less than actively contributing to the devolution of human society. All you are doing, is ushering in the day where history turns against us, and we fail to "make the cut"
In theory, humans have agency. This makes the actual political dynamic akin to a market dynamic, where, bluntly put, people can select sub-optimal product. We see that all the time, in markets as well as politics. However, they can also choose to send a signal that the current offerings aren't good enough. This is to entice a better offering. Sometimes this works, sometimes it doesn't. But at least it beats continuing affirmation of one's support for getting ripped off.
Not only that, but more importantly, it is at least making some effort to align our social construct with the very real Darwinistic demands that do, and will always continue to exist. By this I don't mean a human extinction-level event (although theoretically possible,) but rather the simple fact that institutions, governments, nations, and cultures can die or disappear.
Supporting an aspect of Hillary Trumpkin is just choosing which type of poison to take.
Both major parties have, for quite some time, been in a race to the bottom. They constantly push the bounds of how much garbage they can get away with feeding us, and for some reason the vast majority of us keep choking the shit down, forcing a smile, and asking for another serving.
Your Stein example, while technically correct in terms of mechanics, fails to address the real problem. In fact, that entire mode of thinking is the problem.