We should not allow collection of data about our very close environment, especially home. This will open a direct threat to our well being.
I give you one specific example.
Suppose you have an IoT device in your bedroom that uploads CO2 values (of course it may also do something useful too such us showing this data to you or regulating the ventilation).
Now the rate of CO2 production depends on bodily activities. More activity means more CO2 production. I suppose that you agree that having this information you more or less are capable to deduce when a couple has sex.
This means that we could calculate a metric how much sex is going on and relate it to specific user.
Suppose that we detect that rate of sex has gone down by 20 (a made up number dependant of our model). We can now sell this information.
This information is for example useful perhaps for psychologist who want to sell you counselling.
But it is even more interesting for divorce lawyers who now could prey on couples having period of difficulty in their sex lives.
Even more, this information could be made more valuable by some additional influence. For example feeding the user with articles related to marital happiness and sex life.
I leave the rest for you imagination.