Unfortunate that some have taken to aggressive comments above because I believe this is a serious and significant matter for discussion.
Some carriers, eg BA, Air France, etc, had made a risk assessment of the situation and were not using routes over the area which they had hitherto done. Others had not done this. When just about every
PR statement coming out of corporate head offices starts off with "safety and security is our first concern" we are right to question why some had analysed the position and taken this decision whereas others had done nothing about it.
The airspace over Eastern Ukraine was closed up to 30,000 feet due to war risk, and Malaysian's (and others) flight planning and cost control accountants were happy to accept a routing at 31,000 feet. That's just 300 metres away from a war zone. BA, Air France, etc seem to have decided to keep away by some hundred miles or more. I think it is quite reasonable to ask what part of Malaysian's "safety and security is our first concern" led to this decision, and to subject their risk assessment to scrutiny as part of the accident investigation.
I think we also need to ask MH, having accepted this routing, what procedures they had in place to handle an engine failure, a pressurisation failure, or similar which might require an involuntary descent from the assigned level.
I am aware that there have been (and still are) comparable issues when transiting Afghanistan and similar. I am also aware that very extensive assessments were done of the situation there, regularly reassessed, and there are specific procedures in place to handle any of these events I have just described happening to an overflight there. As far as I am aware none of these procedures had been put in place for any transits of Ukraine.