We don't care about most of the world, as well as "most of the world" knows nothing about Russia.
Of course he had right to invade, more of it - it is his duty.
Some of them just cowards, some of them are patriots of other states. Its ok. Most of them already returned in Russia for safety and comfort.
Are you really interested in the reasons of my personal involvement? Ok. My father was a Jew from Kherson and my mother was a Ukrainian from Mariupol. He was an engineer and she was a nurse. Decent people and members of community. I was born and raised in Aral's region of Kazakhstan, where they have been working. From the very beginning of my life there were two social groups in the town- "Russians" (Russian-speaking specialists, including educated Kazakhs, Armenians, Georgians, Jews, Russians, Ukrainians and others) and not that well educated local "Mambets" (something like Islamistic Hillbillies, mostly local herders). Ecological catastrope of Aral sea, combined with the collapse of Soviet Union and dramatical collapse of the social life raised the worst features of the human nature. Our family was lucky to escape. We found shelter in Moscow region. For a smart boy from hinterland, collapsing in the anarchy and freak show in Mad Max style, Moscow became everything. It is amazing city, best in the world, miraculous and welcoming. I saw what happened in Kazakhstan and other Middle Asia. I saw how peoples are falling in barbarism and civil wars. I know what does it mean - nationalism and religious (especially Islamic) extremism. I know how American, British, Turkish, Arabic "advisors" raise that evil, support it and unleash it against ordinary innocent people. And it was Putin, how saved Russia from this abyss. It was he, who crushed Chechen terrorism, who saved people of South Ossetia and Abkhazia from Georgian nationalists and prevented ethnic cleansings. And it is he, who fight againt pure evil, raised in Ukraine. I believe in equal rights and equal safety for everyone. I believe in human rights and common prosperity. And I believe only strong , united Russia can protect ordinary people from the Western barbarians and inner barbarism. That's why I totally support Putin (and whoever else) in his sacred missions of gathering Russian lands and elimination of barbarism.