I second Malik for what he says, that is to start with!

2nd, actually non of these are really experts in economy! So who cares about what they think!

3rd, Islam does not have a constant economical system (that is an advantage for sure) but it had set the frame that the economy can operate within! So a person who knows these rules very well (i.e. Prof Sharee3a) can come up with plenty of economical systems that are based on Islamic rules (which are very few rules, and again these is a very good thing that few things are ruled and the others are free for the people to decide on it).

4th, Islam should be applied as a whole system, if u were not a Muslim, u are not likely going to give poor people zakah (they might give taxes because they will see projects being done with these money, but to take money from him to give it to needy people is very hard and unacceptable for him)

5th, many banks in Europe are starting to adopt the so called Islamic banking for two reasons:

1- They are more profitable and advantageous for the bank with very little risks. these banks are usually harder for the customers to reach their demands (harder in procedures and requirements)

2- True Muslims will take these hardships just to avoid the Haram interests.

So they really keep bothering me whem they say ISLAMIC BANKING IS THE BEST (for banks yea for sure)

once while driving back from dear Saltus with my dad , we were listening to a radio show on BBC arabia about the same subject ; which economic system is better ? . and they had 2 callers to join and snap on eachother : one from Kuwait but clearly either palestinian or jordanian who supported Liberal system , and another from saudia arabia supporting ofcourse the islamic system.
now this should have been a really cool argument to listen to if it werent for the morbidly ignorant saudi guy who kept on and on that islamic systems are the best and its the solution to everything WITHOUT saying anything else, and it took him 2 minutes to come up with a Semi fully sentence for that matter , while the other guy was clearly more educated and his arguments were powerful and convincing.

what im trying to say that most of the people that voted islamic systems dont have a clue why its the better system and just voted that on pure brainwashing if u will- yes i said it!- and would most likely stutter if u ask them why.