Should organizations enabling cheating be illegal?

In general, I am a supporter of the government staying out of people’s bedrooms. But this morning (stuck in unmerciful traffic), I heard an advertisement for a website that allows people to find people who are specifically already in relationships so they can have affairs together.

This directly infringes on the happiness of an innocent third party (the person being cheated on)—not to mention it violates our social contract (i.e., we have all pretty much agreed that cheating is wrong). So neglecting the nitty gritty of whether this violates any standing laws, do you think this should be legal? Or am I just imposing my narrow-minded worldview on other people’s lives?