Your own links say that it happens, but then hand wave it away as not significant.
Your [1]:
>However, in only 26 cases was there a conviction or a guilty plea by the citizen.
From your [2]:
>n the state of Washington, for example, six cases of double voting and nineteen instances of individuals voting in the name of the dead yielded twenty-five fraudulent votes
From your [3]:
>Although Republican activists have repeatedly said fraud is so widespread that it has corrupted the political process and, possibly, cost the party election victories, about 120 people have been charged and 86 convicted as of last year.
I'm not saying it's widespread, but I suspect that there have been local elections where the outcome was changed due to fraudulent votes. The question is do we care that each fraudulent vote voids the vote of a legitimate voter? And if something such as voter ID requirements were in place, would that have any value? Would requiring states to cross check their voter registration have any value?
As an aside, people seem to enjoy comparing the US to places like Canada and Germany on many different things, health care, progressive tax rates, commitment to green policies, immigration, etc. yet surprisingly no one ever says brings up voter ID, which both of those countries require.