When the Torah speaks of someone becoming tomei, I always thought it was “real” in that a spiritual, albeit non-tangible entity descends or appears to make the person spiritually impure. It’s not just a “mechanism” for instance, to distance a woman from a man during her niddah state. Yet, see the attached Rav Shimshon Rafael Hirsch that seems to state there is also a symbolic tumah. Is he a das Y’chid? What’s the bottom line, and where is the proof (other than the Torah speaks of tumah in many, many places; Is there a Rishon who addresses this issue?
You are asking an interesting question. After reading what he says, if you will notice, R’ Hirsh also says that tumah is real spiritual entity, and a real spiritual existence. My understanding of what he says is that in comparison to tumah that comes to a person because of a more real connection, such as eating something that is tameh, where the tumah now became an essential part of him, and bound with him in a real way. In contrast to that tumah, there is a tumah where the connection isn’t “real” but only “theoretical” because it is only because of an outside contact with the item. Therefore the tumah, since it isn’t “essential” and the bond is not that strong, therefore it can be separated from the person easier.
In general tumah and tahara are real spiritual entities, and have real spiritual ramifications. For example, the gemorah says that a person that eats food that is not kosher, (which the torah says is tameh, as R’ Hirsh explains) gets “timtum halev”, which is a hardening of the heart, in the sense that now it is harder for the person to connect spiritually and emotionally to spirituality. There are numerous stories of R’ Shimon bar Yochai who was able to “see” or feel places that bones were interred, and mark them so prevent people from walking on them,etc. Therefore I don’t think that R’ Hirsh is of a different opinion than the universal understanding of essence of tumah and tahara.