Sharing personal/social information with recruiter or company?

This answer is meant as complement to others rather than standalone. Assuming you appply to tech I strongly suggest to ommit your graduation year, any "era-specific", obsolete skills such as adobe flash, silverlight, vba and etc. Try to not include skills/positions older than decade, unless you are sure that employer is not superficial, values skill and won't judge you as overqualified.

It indeed seems preminilary and a bit prying to ask for contact information of your intimates and other demographic information before you even work at a company. However is there a likely scenario where this information can/will be abused? Especially if it are big and well known companies with a reputation to uphold? Most of this information can probably be gathered from your Facebook profile anyway. I guess it's best to consider these untimely questions just as a quirk that comes with the bureaucracy in large companies. For situations as these, the saying "Pick your battles" was invented. So summarized, don't let a good opportunity pass because of these questions.

I think it's unlikely these established companies are are hiring based on demographic information. However, large companies often have whole departments dedicated to social responsibility. Under this banner they will have environmental initiatives (e.g. drive to be carbon neutral) or charitable goals (e.g. fundraising for a chosen charity or setting days aside to volunteer in the local community).

They are also likely to have socially conscious objectives. These include things like aiming to have women make up at least X% of management at all levels or hiring people with disabilities, from socially disadvantaged communities or from ethnic minorities.

This departments will have goals and KPIs they want to track against. If the company has a reasonably public profile they may want to collate the data for PR and media purposes. That might explain why they ask when your live, your education levels, ethnicity etc.

I don't, however, think this should allow them to request contact numbers of friends and family until you are an official employee when they would need next of kin information. (Unless they were going to call your mom to ask for a reference!). I'd be inclined to politely refuse that information on the basis that you don't have the explicit permission of the friend/family member to give their number to anybody.

Should I share such sensitive information with a company right at the beginning of the recruitment process or not?

Absolutely not. The only reason a company needs your personal details is to know who to contact in case of emergency; until you're actually an employee, they're not going to do that.

What is/could be the underlying reason to collect such specific information?

By far the most likely explanation here is that the "recruiter" is a scam.