system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it often political suicide to "flip-flop" or change one's opinion based on sound argument, evidence, or voter opinion?

It seems like every election cycle this is a negative phrase used by one candidate to the other (both sides being guilty of this). I can think of several times that my personal opinion has been swayed by sound argument, evidence, or strong social movements that I would otherwise not be aware of. 

Thus, changing a political ideology or belief seems like a good thing as it would appear the individual is: a.) listening to arguments and building a sound opinion; b.) listening to the voices of the people and representing the population; c.) has new information on a topic that sways his/her opinion on previous established beliefs. All of these reasons seem to give a person a unique perspective of both sides and allows for civil discussion and debate to continue to occur. Why is this seen as such a negative thing to voters?
gpt
There are a few aspects to this. First is that people like politicians with strong internal principles that they agree with. Bernie, for example, has been hammering the same points for 30 years. You can find old clips on YouTube from the 90s that are almost identical to his campaign speeches. Having strong principles is a selling point.

As a corollary, the worry with politicians changing their mind is that it means they can change their mind about anything for any reason. And there are a lot of bad reasons out there. How do people know you weighed the evidence and came to a reasonable conclusion when you could have just as easily been given a lot of money by a lobbyist or realized there were a few thousand votes to be gotten for a small policy shift? 

It's a fine line. We want politicians that can be swayed by new evidence, but we don't want ones that will cave to anything resembling pressure. But since it's easy to make an ad about flip flopping and hard to convince people that you really did change based on evidence, this is what we get.