The lesser of two evils is not a particularly good decision making strategy. Worse, it is has never been a good argumentative strategy unless it was hoisted up by the side whose evil is so detrimental to the general public that it serves them to try to bring the other side down into the pit with it.
More often than not it is simply a false argument used especially by conservatives with a conscience who are inclined to cast their vote for the more evil side. No liberal or, if you prefer, progressive has ever said liberals and progressive Democrats are without flaws. Right wing conservatives, however, do not hesitate to make or imply those claims about themselves.
When the flaws of the conservative party become indefensible, even for them, swing voters and conservatives voters with a conscience who want to vote for evil often will attempt to allay the pangs of conscience with the statement that both sides are guilty of the same things. But some sins are greater that others. Moral democratic depravity and sociopathic intent for the purpose of denying civil rights and the pursuit of happiness for American citizens makes a big difference.
Many of the voices of the conservative right such as Fox News, Rush Limbaugh, and some members of congress routinely engage in rhetoric that borders more on the behavior of a sociopath than it reflects the proponents and supporters of The United States Of American and American Democracy. If you have doubts about the veracity of that statement consider the characteristics and rhetoric of the loudest conservtive voices.
1. They seem incapable of feeling shame, guilt, or remorse for any of the things they say or do. They lie even when it is obvious that they are lying. They never apologize or ever allude to the fact that they could possibly be wrong about anything.
2. They will do or say anything to win and hold on to power even to the detriment of the entire country they profess to love. We should never forget: "I want Obama to fail even if it means America fails." After which, the anti-Americans anti-democracy sociopaths in congress did and are doing their best to make it so.
3. They are delusional and are served by delusional followers, even to their personal detriment . They believe that every lie and false accusation they make is true because they said it or that it becomes true if they say it enough, which they do ad nauseum.
4. Unlike the founders of this great country, conservative sociopaths hate the common man. Even though the founders were wealthy men, they had a vision of a nation and framed a constitutution that promoted the general welfare and not just the welfare of the richest 1% or the richest 5%, etc.
So when conservatives and swing voters with a conscience who vote for evil right wing conservative Republicans because they reason that both parties do the same thing and that they are voting for the lesser of two evils, they are voting against...
1. A Democratic Party that created the Great Society which included work study and Pell Grants that helped millions of American get an education, many of whom went on to create new businesses.
2. A Democratic Party that gave us medicare, social security, the right of women to vote, legalization of interracial marriage across the USA, anti-discrimination laws that protect Americans from being denied housing, jobs, etc. on the basis of race, sex, sexual orientation, and religious affiliation.
3. A Democratic Party that gave us Affordable Health Care and are allies on the side of democracy against the war on women and for protection of LGBT, immigrants, and other minorities.
There are many more benfits Americans have received as a result of having a progressive Democrat in the White House and/or a progressive Democratic Congress.
Equally as important as remembering the benefits of a progressive Democratic Party, Americans should remember that today, tomorrow, and likely forever, right wing conservative Republican sociopaths and their sociopathic Tea Party confederates insist on taking those same rights and benefits away from you.
Conservative sociapaths want working class Americans unhappy, broke, needy, and without safety nets. That is not the lesser of two evils; that is evil personified. That is evil that should be kicked out of office and not allowed to pretend that it loves America, Democracy, and the American people.