Everyone knows the power of chumra to divide people. In the past we have discussed the problems that can emerge because of yuhara (here), lo taaseh aggudot aggudot (here), and other issues. However, sometimes chumra can be used as a way to unite a community, as can be seen from Rabbi Moshe Feinstein’s treatment of chalav stam yisrael. The shiur and sources can be found: here.
The Gemara prohibits a series of products and interactions with non-Jews. Some of those are prohibited because of concerns for chatnut, roughly translated as intermarriage, though the actual definition is probably more expansive. Others are prohibited for concerns of kashrut. The Gemara entertains other explanations for some of these prohibitions as well. One of the prohibitions is that of chalav akum, milk that was milked by a non-Jew. The Gemara limits this to cases where there was not a Jew watching the milking, or at least sitting outside where he could in theory come in and see. The Gemara suggests that this was instituted to prevent the mixing of non-kosher milk, though there are commentaries who assume that it was also for issues of chatnut.
In general, there are two main positions as to the extent of this issur. Some have limited it to cases where there is actually a concern of non-kosher milk being mixed in, therefore excluding cases where there are non-kosher animals in the city. This is most famously held by the Pri Chadash, and was later adopted by Chazon Ish. The upshot of this position is that you don’t need “chalav yisrael”, you just need milk with no concern of kashrut.
Others assume that it is a formal prohibition which goes beyond the motivation. Thus, even if there is no concern of non-kosher milk being mixed in, it is prohibited. This is the position of most poskim. The opposition raised to the position of the Pri Chadash has been fierce. The Aruch HaShulchan goes as far as to tell a story of a person who relied on the Pri Chadash, only to discover that boiled animal brains had been mixed into his milk. He uses this argue that not only is it a formal issur, there are many more reasons beyond those listed by Chazal, so it maintains as a substantive prohibition even when you might think it does not. The upshot is that you need something called “chalav yisrael,” not just concern free milk.
Here enters Rabbi Feinstein in a series of teshuvot. He was presented with the issue of industrially produced milk, what he called chalav companies, what is commonly called chalav stam. Under government regulations, it could not be anything by cow, i.e. kosher, milk. Rabbi Feinstein argues that even if we reject Pri Chadash, which he does, we can still permit industrial milk. He argues that the concern of being exposed for lying, which would incur fines and would bring about terrible publicity, is so great, that we know that there is no non-kosher milk. He then argues that knowing is like seeing – so our milk is actually watched by Jews, so to speak. In other words, it is chalav yisrael! He maintained this position even after being told that the fine was minimal – he thought the threat of bad publicity and the like was great enough to assert that we know it is kosher. He proves that knowing is like seeing in this context from the fact that we never really need a Jew to see the milking – if he is outside and creates fear it is good enough. He also shows how in many other cases we treat knowing like seeing.
What emerges is that Rabbi Feinstein rules that chalav stam is actually chalav yisrael. That being the case, if one agreed with Rabbi Feinstein it would be permitted lechatchila to drink this milk, though if one argued, it would be prohibited. Rabbi Feinstein here suggests, however, that there is value to being machmir and only drinking chalav yisrael mamash. This move makes very little sense legally. If he is correct, all milk is chalav yisrael. However, from a policy perspective, this is brilliant. He creates a category of keeping the issur as it was kept classically, and recognizes the value in keeping the issur this way, even if legally there should be no difference between “chalav yisrael” and “chalav stam.” He then writes that those who keep the chumra (himself included) should be praised, while those who don’t are keeping the ikkar hadin. In other teshuvot he encourages schools and similar institutions to be machmir.
By creating this new type of chumra – he actually united the entire community behind his psak. Those who wanted to drink chalav stam could legitimately say Rabbi Feinstein said it was totally fine. Those who wanted to drink chalav yisrael mamash could also say that they were following Rabbi Feinstein. Thus, all of Klal Yisrael would say they were following the same psak even while doing different things. Rabbi Feinstein has other cases where he does this. This brilliant move allows for unity by creating and legitimizing various ways of keeping Halacha, thus showing that chumra does not only divide, but can unite.