This is the kind of mindset that keeps people from voting third party.... "You're just throwing away your vote" and it's a self-fulfilling prophecy, because enough people believe it, and either don't vote as a result, or vote disingenuously, that nobody votes for third parties that they actually want in office.
The problem is self reinforcing too.
The fact is, if enough people are brave enough to "throw away their vote" by going for a third party, the momentum may push others that either are not voting, or are voting for a party they don't believe in, to vote for the third party that doesn't normally have a chance, to actually add their voice to the mix and those people may be enough to actually swing towards a third party.
This rhetoric is the exact same crap that OP is complaining about.
I understand why people don't want to "throw away their vote" on a candidate that isn't likely to win, which is why we need voting reform and an alternative to the FPTP voting that we currently "enjoy", so people can vote for who they actually want, and still not "throw away" their vote if that candidate doesn't get enough votes to get in.
Which makes it even more important for the right to maintain the current voting system. By gerrymandering the hell out of the districts, they can dilute more centrist and left-leaning areas into several strong conservative areas nearby, or concentrate undesirable voters into a single district, which is vastly out voted by the surrounding districts.
The whole thing has been manufactured to optimise the capacity for success for those who do not win the popular vote.
IMO, it's insane that a party can consistently win the popular vote, but not consistently win elections. It's crazy.