Behrooz jaan, as civilized people international laws are all we have going for us and as civilized people we should all expect and in fact demand from our governments not only to act within the boundaries of international laws, but to uphold them and speak for them where and when they are being broken, regardless of who's doing it. If previous US administrations have broken international laws, they have been judged for it by the world's inhabitants - that fact should not be used among intelligent people to justify another country breaking international laws.
I did not support US invasion of Iraq and I do not support what Russia is doing in Crimea. I did support a UN mandated attack on Afghanistan and I did support Russia in its war against Georgia. Right is right and wrong is wrong - don't let politics and politicians define your principles as an individual.
Having said that, all people in this world have a right to self-determination and that includes Crimeans. But you can NOT hold a referendum at gun point or under duress, nor can you completely ignore the constitution of the country you currently belong to, or the political will of its people. The Crimeans have every right to hold a referendum, but not without the support of the Ukrainian government. The parties need to sit down together and sort through this mass with a negotiated solution that will be satisfactory to everyone with a potential referendum in due time - perhaps in 2 to 3 months. You need to provide the right amount of time and notice to people who want to move out, because they too have a right to self-determination.