Ukraine reacted as most countries would if some party or party group was trying to undermine it and take away part of its territory.
Yes, more or less. But they went further and sent not only regular army, but also battalions consisted of criminals, who are terrorizing the locals.
Also, not every country would bomb onto own cities, including schools and hospitals (Ukrainian weapons are not too accurate).
How people after that would want to live in such "ordinary" country?