For those unfamiliar with what happened in Lithuania, in 1991 Gorbachev used military force to kill 14 Lithuanian civilians who were demonstrating for democratic reforms.
https://www.rferl.org/a/lithuania-soviet-crackdown-1991-krem...
replies(1):
https://www.rferl.org/a/lithuania-soviet-crackdown-1991-krem...
You seem to comment to better inform readers, yet your comment distorts the truth.
Even the article you linked talks about Lithuania declaring independence from the USSR, not asking for democratic reforms.
Despite what your article says, if you read the story on Wikipedia, Lithuania did in fact unilaterally declare independence from the USSR in March 1990.
Just as an example, check what Spain did in 2017 when Catalonia tried to declare independence after a popular vote. If Catalonians decided to resist, there is no doubt that the Spanish state would have used violence to suppress them. Try to imagine what the USA would do if any of its states tried to declare independence.
The Bolsheviks wrote a constitution providing for a "union state". I doubt the framers of the Soviet Constitution actually meant what they said – it was essentially propaganda to present the Soviet Union as some kind of "voluntary association", despite the reality that there was nothing voluntary about it. While it was a federation on paper, its substance was much closer to that of a unitary state.
When the Soviet Union collapsed, the seceding union republics used their constitutional status to justify their secession as legitimate - they took the constitution's pretence literally. But, imagine in an alternative timeline, the Soviet constitution had been written without this pretence–would that have stopped the Baltic states from seceding? I really doubt it. Would it have made any difference to the legitimacy of their secession? Only on meaningless paper.
Even with the Soviet Constitution we actually had – why did the Union as a whole break-up, but not the RSFSR? That question is better answered in terms of real world power structures, than legal formalities. Chechnya fought for independence, and if Moscow had been weaker, they could have won. Even now, some would say that Ramzan Kadyrov rules Chechnya as his own quasi-independent fiefdom, and is just biding his time for the right moment to officially claim independence (maybe, if Putin were to suddenly die without a clear successor). If Chechnya were to successfully secede, that could inspire other parts of Russia to seek to emulate its example.
> Meanwhile USSR constitution had such article. Which was used by Lithuania when declaring independence.
Source?
I can't find any article detailing an exit process in the 1977 USSR constitution. Only at the beginning it says that the USSR is a voluntary union, but that's far from saying it details an exit process.