In 2000, many Democrats said that Ralph Nader took votes from Al Gore in Florida making it easier for George W. Bush to become president.
In 2010, Tony Sutton, chair of the Republican Party in Minnesota, said that Tom Horner, Independence Party candidate took votes from Tom Emmer, allowing Mark Dayton to become governor of Minnesota.
Maybe both complaints are misdirected.
In either case, have they considered that many of the people who voted for the "minor" candidate might not have even voted if they hadn't had a third choice?
In the 2010 Minnesota governor case, has anyone considered that Mark Dayton might have "taken votes" from Tom Horner? Maybe many voters would have voted for Tom Horner, but they didn't want to "throw their votes away" and allow Tom Emmer to become governor. So, maybe they voted for Mark Dayton because they thought he was a better choice than Tom Emmer.
Unless we interview in depth every single voter, we'll never really know their motivations. It really is presumptuous to assume to know the intent of unknown voters.
