Without knowing the specific circumstances it's unsound to comment one way or the other. However I would note that destroying the cubs would be acceptable in two situations involving cases where the mother was killed for being a known man eater, or destroyer of stock:

i. Cubs that are too young to survive on their own would need to be destroyed rather than have them slowly starve to death.

ii. Especially in the case of man eaters, cubs may have learnt to associate humans as prey and need to be destroyed to prevent them being a future threat.

I'm not claiming either of these situations was in play in these photos, just that I wouldn't rush to judgement. I also note that the primary reason for the decline in tiger numbers isn't hunting, but rather habitat loss affecting both tigers and their primary prey species.