The Midianites presented a major threat to the Children of Israel. They had rejected any form of compromise or accommodation. Balak of Moav, an ally, had brought Bilam the magician to try cursing. When the supernatural did not work to stop the advance of the Children of Israel, the Midianites turned to sexual tactics.
Actually, there is a tradition that they did so on the advice of Bilam, which would be another mark against him but doesn’t seem to follow the text which has Bilam accepting that what God wants, He should get. Having experienced the special relationship between God and Israel why should he try challenging the clear will of an Almighty power he accepted? Unless you assume that, like Satan in the Book of Job, he had been “given permission” to test the Hebrews.
The Midianites sent in their sexy women. And they were hugely successful, not just sexually but in seducing many of the Hebrews into idolatry and the worship of Baal Peor. “Peor” literally means defecation. The orifices of the body were used as part of religious worship. Defecation and sexuality coming from a similar physical source are then equated within the framework of religious worship. Peor is known for its temple whores and the requirement that every woman be prepared to prostitute herself as an act of religious submission.
Of course, this approach to life fundamentally contrasts with a spiritual one in which the physical is restrained and combined with a different dimension. The fact that chieftains, the most senior level of the Hebrew hierarchy, were seduced to the point of publicly defying Moshe meant that the threat was a very real one. But does this justify the extent to which in this week’s reading the Children of Israel were commanded to purge themselves of this evil influence? Even to the point of having to purify the vessels and cutlery of the Midianites?
This indeed is the origin of our custom of kashering and toveling (immersing in a mikvah) vessels and implements used for food. This origin underlines another important dimension of kashrut; we need to combine the physical with the spiritual.
We do not reject physical pleasures, but our tradition requires us to see them as part of wider, deeper, spiritual world.