There's only one word required here....regulation
It seems ridiculous that these low life companies are beyond legal recourse whereby they ask people to work for them for free (although equally the pilot is as culpable!!) I have seen this sort of rubbish before, and in fact in one instance the company were taken to task by the department of employment for not paying employees at least minimum legal wage. The pertinent word here is EMPLOYEE. This said, there are always going to be areas of the world where immoral and unethical things like this happen.
Its bad enough that people are being made to pay for their own training / TR. That to me indicates no commitment at all from the employer, which in itself breeds a very bad, intrinsically dangerous attitude. To take it further and work for free for 18 months in a so called professional airline operation is just plain nuts and is diluting future terms and conditions for all of us.
Its a totally short termist view and personally I wouldn't do it.