Why are some people careful to drink only 'chalav yisrael' and others not?
Historically, there are only 2 categories of milk: Jewish milk and non-Jewish milk. Non-Jewish milk was forbidden by the Rabbis out of fear that it's not 100% cow's milk, rather the (forbidden) milk of a non-kosher animal was mixed in.
Jewish milk was defined as milk which a Jew witnessed from the time of milking.
There was no 'middle category' of 'stam chalav' - it's either Chalav Yisra'el or it's treif.
R' Moshe Feinstein (IgMo YD I:46,47,48, 49. II:31,35,47,48. III:16. IV:5) explains that the threat of legal ramifications for adding non-cow milk generates a situation where we KNOW that the milk is cow's milk. What R' Moshe is saying is that in the USA, generic milk IS chalav yisra'el. There's no third category.
Those who would still be makpid on milk that was actually witnessed by a Jew the whole time, are doing so as a chumra. My question is - why? If R' Moshe's right, what would one gain by staying away from generic milk which is, essentially, itself chalav Yisra'el? Is it to cover the bases, since there are opinions which disagree with R' Moshe's? Is it 'middas prishus', a general impulse to restrict what we can eat?
One thing R' Moshe definitely didn't think it is: a status symbol.
I also find it incredibly interesting that Chalav Yisra'el, which is COMPLETELY supererogatory, is a very popular chumra, whereas Yoshon, which is an actual halakhic issue and a very problematic 'hetter', isn't nearly as popular. Same goes for 'gebrokts' - it's a fad to keep gebrokts, though it's a complete and total 'minhag shtus' (not my formulation), but try getting s/t certified KP if it's gebrokts. But Yoshon - pfff. Pass the cookies. I don't keep yoshon (perhaps I'll post about why at another time); I'm just intrigued by what gains currency in the world of religious one-upsmanship (ok now I'm rambling; this is getting into issues I discussed here).
So remember. You heard it here first. Baskin-Robbins is Chalav Yisrael. So is Friendly's (and Edy's, Haagen-Dazs, etc.) . I like the pistachio almond. Enjoy!