This is like being neutral between a robber and his victim. Anyone who is "neutral" in an election between a Republican and a Democrat is -- in the eyes of any Republican -- helping the Democrat by not helping the person trying to defeat the Democrat.
A vote for the Republican helps the Republican
A vote for the Democrat helps the Democrat
A vote for a 3rd party helps neither the Republican nor the Democrat - it is neutral.
By your logic, a person who votes for the Green party is helping the democrats.