Where did the practice of making a double hole like a tzeirei in the beged for the tzitzit originate? Why would someone have a different practice for a tallit katan and tallit gadol?

It is al pi Kaballah, and it is not "proper" to display to the world that you are noiheg al pi Kaballah, so it is not done on a Talis Godol.....

But don't a lot of those guys wear their tallit katan exposed, at least on occassion?

Its a chasidish minhag. My last pair had them and everyone wanted to know if I was chasidish.

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Actually it is not only for a "kabalistic" reason. see the Magen Avraham (and the bach, both of them were not chassidim, neither was the baal haitur for that matter) Siman 11 SK 13

So basically it's a chumra and it's yuhora to display adherence to this chumra?

Yeah.

The question is, if a whole segment of jews do a certain "chumrah" without them even realizing that they are following a chumrah is that also yuharah? everyone knows that they just bought their tzitzit from the store.

Interesting question. First of all, if a lot of people do something such that it's normative, it's not yuhorah anymore. That's the excuse, for example, for "simpletons" to wear R"T tefillin in spite of what the Shulchan Aruch has to say on the topic.
Second of all, on the subject of people not knowing if what they are doing is minhag, halachah, chumra, or other, then that's a whole other topic. I suppose if simpletons are just wearing what their Outreaching mentors tell them to, then maybe it's not yuhorah.

I was not even getting in to the "outreaching" issue. I was referring to those "already there".

The argument stands. If someone is just buying something without understanding the issue behind it, let's say he's just following social convention or copying what he sees other doing or pulling the first thing he sees off the shelf, then I don't see how it's yuhorah. It's simply being a simpleton.

It was not an argument. however I was trying to keep the outreaching issue separate, since I think there are various other issues and variables that come into play once you start talking about "outreaches".

Thats me.

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