I am not questioning the validity of that statement but I hate this so much. It's like brainwashing on a mass scale that if you don't vote for one of these two crappy parties you're throwing your vote away. The GOP / DNC have convinced so many people of that, just to keep any viable third party from trampling on their political power.
It's not the Republicans and Democrats to blame for this--it's a reality based on our electoral system (forgetting about even the Electoral College for a moment). In a first-past-the-post system, all that matters is reaching 51% in one vote. In such a system, this situation is guaranteed to happen.
First of all, you can't have more than two viable parties when most (even if not all) people identify across a conservative/liberal spectrum. If a new party were to emerge, it would be seen as either more liberal or more conservative. A more liberal party would split votes with the existing liberal party, dooming both. A more conservative party would split votes with the existing conservative party...dooming both. The only stable situation is one major party for each ideology.
Second of all, once you're in that situation, a voter who doesn't like either party is faced with a choice: vote for a third party they like more but has no chance at winning
or vote for one of the two big parties that is closer to what they believe and has a chance of winning. The first option represents them better. The second option gives them some voice in government. It's a tough choice and most people take the second option because they want some say.
There are other, better systems. Like run-off votes, where you hold the first vote with all the candidates and then hold a second vote with just the two top vote-getters. That removes the above choice: someone who doesn't like either of the two big parties can vote for whomever they like in the first vote, allowing third parties to slowly gain a base of support, and then vote for whichever of the two big parties aligns closer to their views in the run-off. They get to express their real choice
and get representation in who eventually runs things. And maybe one day, one of those third parties will be among the top two vote-getters.
There are other systems, like ranked choice voting. Plus, of course, parliamentary systems, which tend to be friendlier to smaller parties because it's not all or nothing when it comes to a leader--all sorts of parties can, and often do, have some representatives in parliament and it often takes coalitions of parties to create a controlling bloc. Obviously, a parliamentary system isn't going to happen in the US in the foreseeable future. But blame our system for independents and third parties being viewed as "wastes of a vote." Because, in our system, they are wasted votes
if you want a voice in who's in control.