It's not an opinion when one states that NATO was created primarily to fight the Russians and that it is strategically, and operationally geared for that role. It's also a fact that it generates an immense amount of money for American and Western European defense contractors. Especially American weapons manufacturers. It's a cash cow. Why should Russia allow Ukraine to turn itself into a launching pad for NATO, threatening its security?
"The North Atlantic Treaty Organization was created in 1949 by the United States, Canada, and several Western European nations to provide collective security against the Soviet Union." Source: https://history.state.gov/milestones/19451952/nato#:~:text=The North Atlantic Treaty Organization,security against the Soviet Union.
More, why should Russia allow Western Ukrainians under the influence of Washington, to establish a puppet regime in Kyiv that is Russophobic and anti-Russian, undermining its interests in the region? Western Ukrainians along with ultra-nationalists, with plenty of support from the US and its allies, ousted its democratically elected neutralist Government in February 2014, with a rabidly anti-Russian Government. Yet more than half of the country was for president Yanukovych, and lean ethnically, linguistically, economically, and politically towards Russia, not the EU or the new Western-backed regime. The US and the Ukrainian Russophobes and haters created the conditions that led to the war we're seeing now between Russia and Ukraine.