None of the nuclear powers can be invaded. Intervening in Ukraine is one thing and invading Russia is another. If the UK and US send their troops to Ukraine, it will not necessarily start the WW3. On the other hand, if they send their troops to invade Russia, it will definitely signal the start of WW3 and MAD. Russia will definitely use some of its 10,000 nuclear war heads and half the world will turn to radio-active waste land.
I agree, nobody is stupid enough to start world war 3. The proof is in front of our eyes- the Korean War, the Vietnam war, the Soviet Afghan war, and now Ukraine... the West and the East will only fight each other through proxy wars meant to empower each side and/or take advantage of a war-wrecked country.
The reason the West demonizes Russia (as it has for well over a 100 years, as you suggested) is because governments love to create enemies to keep people in fear and away from the real issues. You have Russia doing the exact same thing. Hell, this is like the #1 rule of international relations - every country points the finger at someone else to make themselves out to be the heroes and keep their populations ignorant of the real problems in THEIR OWN country.
The conflict in Ukraine is just another proxy war, as the many we have seen in the Cold War. Nuclear weapons have made large-scale,conventional warfare entirely obsolete, and I hope it will stay that way. Leaders of countries may not always be the brightest and most peaceful individuals, but everyone understands that REAL nuclear war will destroy not just the enemy but also you. MAD keeps the world from another great war, at least for now.
. After all the debates we had on the subject