Companies sponsoring H-1B employees are required to offer them a fair salary, which is meant to prevent cheap labor importation. From wikipedia's H-1B article:

Employers must attest that wages offered are at least equal to the actual wage paid by the employer to other workers with similar experience and qualifications for the job in question

Just as we don't like species going extinct because of the potential medical and scientific discoveries they might have helped attain, languages are useful in that analysing them help us understand the human language faculty and by extension the human mind. So a diverse language ecosystem is very important in that regard. OTOH, it's hard to justify preventing/discouraging a population from adopting a more dominant language, since it might well be that doing so will give its members better work opportunities for example, or otherwise allow them to attain a better quality of life. Linguists mostly agree that the fairest solution to this problem is to record as much as possible about the language before it's gone foreever, while otherwise letting nature take its course.