Main alternative (not FLOSS, but European) would be XING! as far as I know

Because every piece of data they have on you can (and will) be used to manipulate (and hence control) you. Make you buy products you don’t want, think things you wouldn’t have thought and do things you wouldn’t have done. Are you aware of how much they control what you see, hear and read? Do you not think they would leverage this power to their advantage?