Iran has been trying to hijack oil tankers and shipping (in international waters) for years. It's been on TV documentaries like "Warship". The Houthis' are armed and backed by Iran. The real Yemeni government support this action and quite obviously want rid of the Houthis'. As has already been said, they aren't just attacked OUR Navy, it isn't Yemen we are targeting and this isn't just about shipping to Israel (which is what they said it is).
It's quite right we have in the past gotten involved in things in the middle east when we should not have, however when you have countries attacking shipping that half the world depend on for Oil supplies and goods in international waters.. then someone must act. And as usual since the US and UK are one of the very few countries that has any ability these days to do anything more than a few hundred miles away from home.. we have.
So civilian lives in the ME don't matter as long we can get cheap goods from China.
Millions of people around the world marching for peace and we start a new war.
We haven't hit civilians, we've hit the Houthi's supplies. The Houthis do not equal Yemeni's.
We haven't started a war but it feels very much like Iran wants to start one.
It isn't just our goods, it's half the worlds goods and oil and gas, and the ability to freely travel in international waters. That means something.