"Are Arabs even capable of democracy?"
Well, they said the same about Germany and Japan 66 years ago...
Germany managed to adopt democracy for several reasons :
1) it is a Western country, part of the same civilization, sharing similar values as countries such as France, Britain or the USA. Arabic countries just don't share these values and common history.
2) The USA, Britain and France helped Germany set up a democratic system adapted to its cultural specificities after WWII, taking into account the weaknesses of the failed experienced of the Weimar Republic. There was a strong will from the Allies that democracy worked in (West) Germany to avoid another war, and they did all they could to make it work.
3) Germany was heavily culpabilised for its responsibility in WWI and WWII, as well as the Holocaust, which helped the self-conscious Germans to try as hard as they could to prove to the world that they could become a peaceful democratic nation too.
4) The EEC, then EU thoroughly encouraged the development of democracy in Germany. Contrarily to Japan that was isolated from the Western political scene, and could do more or less whatever it wanted, Germany was at the centre stage of the Western world during the Cold War (in part also because it was divided, and Germany acted as the showcase of the Capitalist vs Communist systems). As a founding member of the EU, Germany had little choice but to become a role model of democracy. Its political scene was observed by other EEC/EU members. When you feel watched from the outside it is always a good incentive to show the best you can do.
Japan, on the other hand, failed to become a true democracy. It developed well economically, but under a rather autocratic single-party government. Even today, Japan is only an illusion of democracy and Japanese people will be the first to tell you so. It is democratic in the sense that China sees itself as democratic (an elected paternalistic government that cares about the people rather than the own self-interest of a despotic monarch).
Personally, I do not hold the view that a country is democratic so long as its government is elected. There must be a plurality of party to represent the various views of the population. Nowadays too many democratic parliaments and governments are like appointed boards of directors, chosen among the ranks of a small oligarchy, divided in one or two parties that hold basically the same views (like in Japan or in the USA), or anachronistic parties that are completely out of touch with modern reality (like the French extreme-left or extreme-right that both want France to quit the EU, revert to the Franc and live in autarky).
Another issue is that these revolutions came from the Arab people, so this is not something that is pressed onto them from the outside.
The revolution came from the Arab people, but against the Arab people that oppressed them, so it doesn't mean anything. Besides, if no "experienced" democratic country is behind them to "guide" their democratic reforms and help them set up the right institutions, there is a good chance that things won't be done properly. In 1789, French philosophers of the Enlightenment helped setting up the first (yet very imperfect) European democracy, the world's first declaration of human rights, and so on. North African countries do not have Enlightenment philosophers among their ranks today. In 1945, the Germans had the USA, UK and France behind them to help them set up their democracy, then the EEC/EU to foster its democratic development. Arabic countries are not part of the Western world, and do not have any democratic organisation like the EU to keep them in check. I believe that none of the elements that allowed the success of democracy in Europe exist in Arabic countries, and therefore democracy will fail.