I don't get the hysteria surrounding the sinking of IRIS Dena. Neither the Dena nor the US submarine that sank it were in Indian territorial waters (or in Sri Lankan waters for that matter).
The US & Israel are pounding to pieces any offensive or potentially offensive Iranian military capabilities within that country, but for some reason an Iranian warship has to be left alone because it's not in Iranian waters/out of theatre at the moment? That doesn't make any sense. Once hostilities with a country are open, if you have the capability to destroy that country's military assets before they can become a problem, you do it.
And what's this about 'fighting fair'? War is never fair, the whole point of war (and preparation for war) is to ensure that you give yourself the most unfair advantage you possibly can.
Besides, the way I see it - the IRIS Dena was a POTENTIAL THREAT waiting to manifest itself. It's obvious by now that Iran's military is targeting countries without rhyme or reason, in an effort to increase the cost of war on as many countries as possible (including nominally unaligned parties like Oman, or even those who were aligned with anti-Israel causes like Qatar), so as to indirectly pressure the US & the world to stop the attacks on Iran.
Knowing this, how can anyone guarantee that IRIS Dena wouldn't have eventually targeted shipping in the region if & when ordered to do so? If not attack one of the countries in the region in an effort to impose costs on them so that they in turn apply pressure on US? Several Indian mariners have already lost their lives due to Iran's attacks on civilian shipping.
Waiting for such an eventuality to come to pass would have hurt India's and our southern neighbour's economic interests much more than what the closure of Hormuz is already imposing on us.
Bottomline, I don't see why this is even a big deal. It's just 1 ship among 10+ other Iranian ships that were sunk over the last few days.