I have read that skinnier smooth tyres are actually safer than knobbly mountain bike ones because of contact area and the grip comes from the road gripping the tyre as opposed to the tyre gripping the road, unlike a car. After all, you're not using a mountain bike for it's intended purpose?

Is your other half a cyclist?

I found my fiance was worried about me being interested in a road bike but he is a non-cyclist and didn't understand the differences. The logic was thick, knobbly tyres = grip. Often on the road this isn't true.