Putting too many ideas together at once can ruin them. Ideas need room to breathe. In this case, two perfectly normal ideas are forced to share a single handle to save space, time and material. But it is clearly a toxic combination. The presence of a toothbrush on one end may not affect the toilet cleaning function; but the presence of the toilet brush destroys the usefulness of the toothbrush. This kind of interaction is important to consider when designing things.
If we take a smoky room, and start adding nonsmokers to it, it has no effect on the air quality. But start adding smokers to a room with clean air, and each smoker contributes to destroying the air quality.
This is a directional effect. In one direction the effect is nothing; in the other it is everything. Smokers, noise makers and other polluters miss this point when they argue for laissez-faire equality. They try to equate things that are not equal. Adding a spoonful of vanilla pudding to a bucket of sewage does not turn it into vanilla pudding. But adding a spoonful of sewage to a bowl of pudding does turn it into a bowl of sewage.