I wouldn't talk about slave labor - I'm fairly confident you'd get some compensation. Also, I'm guessing that if you show up somewhere with I've worked at CERN in your CV, you get some extra points.
Actually, that's the modern path of passage. Do it all for very little for "extra points CV"... I have over 10 years of experience and recruiters are still trying to convince me that I will benefit from being able to add this superb company to my CV. HA! HA! My short CV is 16 pages long and on the list of companies there are JP Morgan, Visa, Cartoon Network, BBC, Payboy, Sony...
The larger the company the less they think they can pay. Be pragmatic and don't let be pushed around. On the other hand, if you have no experience - shut up and be grateful for any wisdom you can get without paying for