Advisor won't let student do an internship

I am graduate research assistant in Computer Science in the US. A while ago, a master's student in the research group, who plans on a career in industry after graduate school, received an internship offer from a large, well-known technology company which is one of the most sought after and prestigious opportunities for any Computer Science student. An internship at a company such as this would be extremely valuable both in terms of shining on his resume and the experience he would gain there. This internship would be a huge break for him and could really launch his career. However, when he asked for his advisor's okay to take the internship for the summer, his advisor told the him that he would have to find someone to replace him to continue work on the research project which would essentially mean the student would lose his funding when he returned from his internship. I have two questions regarding this situation:

(1) Is it unreasonable for the advisor to not allow his student do an internship at this company when such an internship would be tremendously valuable to the student's career, or is the professor right to ensure work continues on the research project even if that means cutting this student's funding and finding another student to take his place?

(2) Given that the Master's student plans on pursuing a career in industry, should he take this prestigious internship anyways even if he loses funding because of it?