Nev,
“You’re implying that we should just follow the letter of a law, and if somebody wants to take on one chumrah as a nice thing, they have to take on every chumrah that exists? That’s absurd.”
Yes – Read my above comment on how and when you can pick a certain Halacha as a “Ba’al Nefesh” , otherwise, why is R”T teffilin the only point where you say so – why wouldn’t you apply any other Chumra to ” Mechza “k’Yehora” ?
FYI – “Ba’al Nefesh” is a certain level you have achieved as a Yirai Shomayim – it is across the entire spectrum of Halacha. You don’t exactly pick and chose, unless perhaps you have a specific reason to, as above.
Rashi in Pesachim 40a says:
“בעל נפש – “חסיד:
הכי קאמר אפילו חיט – ….. בעל נפש לא ילתות אבל” דלאו בעל נפש “דלא מחמיר על נפשיה כולי האי”: דשרירן.:
This is across all halachos – not one or two.