Peaceful decades in human history were breached when US invaded Afghanistan, Iraq, Libya, tried to overthrow Assad. Now Putin is bad because he responded to a call for help from Assad. Assad is still legitimate president of Syria by the way, it's the rep of his government represents the country in UN. As mentioned earlier Russia have a military base there and are making sure it stays there.
As for Crimea, if anything, it is the closest comparison to "the good intentions" that you mentioned. A referendum was held, not a single bomb dropped. Came back from there a little over a week ago. Fantastic hotels, not a signle refugee. Again, I do not support what Putin did, but it cant be compared to Afghanistan, Iraq, Syria, the overthrow of Gaddafi. Millions dead, refugees all over the Europe, countries that will hardly be rebuilt in decades to come.
NATO's expansion towards East, extremely close to Russia's borders, the withdrawal of US from ABM treaty in 2002, and you expect Putin to do sweet feck all about it. No way.