I have one issue with the "centrist" description and that is that the political center shifts as the mainstream veers towards the left or the right.
When people say "centrist" do they mean someone who is at the centre of the entire left-right spectrum as measured by the actions of left and right wingers from the 18th through to the 21st century or do they mean "at the centre" of the views of mainstream political candidates?
The latter changes as viewpoints and policy norms shift over time, to say nothing of different views of what "left" and "right" mean in Europe, Asia, Oceania and how these contrast sharply with what is perceived as left and right in the US.
A libertarian, socialist or liberal will have broadly similar views on social and economic policy in almost any historical or geographical context, a "centrists" position is entirely contextual on where the political "middle" has shifted to in their time and place.
First of all, you're implying that updating your position to accommodate new understanding is a bad thing.
Secondly, you're being disingenuous and ignoring a concept called "context." You don't have to necessarily be a centrist on everything. A centrist could just be someone who sides with both parties at different times on different issues - and I'm not just talking about one or two issues. You could arguably also imply context by the person, issue, and time. Of course politics aren't static. That's why concepts like "context" exist.
Also, we're talking about a political spectrum here. Most issues have many components, how you fall on them depends on your views of each component. You can't just say you're left or center or right. There are different degrees of "leftness" and "rightness." There's also different degrees of "How much are you willing to support a stupid - or at least flawed - argument because it matches your ideology?" Remember that the flawed arguments could be strengthened with other arguments, depending on what they are and what they can be supported with.
I just see so many people willing to die on an issue hill because they think they're right and are too stubborn to considered that their argument or case isn't as brilliant as they thought. Their political beliefs are dogma that they never approach with any skepticism.
I guess I think centrists are just a bit more willing to put their own beliefs to scrutiny. They're also willing to modify or abandon their beliefs if they think they don't past muster.