Pederas,
I think there are several problems that have been pointed out but it comes down to preference and price. Personally I like solid wood cabinets, but I build my own. I'm not that crazy about working plywood or MDF, but that's my preference. Price on the other hand is what has caused such a disdain by many for MDF. To many of the cheap cabinets are made of cheap MDF or particle board even LDF with thin plastic overlay. MDF and MDO has been around for a long time and good quality cabinets with a good finish or veneer have been made from both. Unfortunately most people can't see the difference so they equate one with the other. The price, manufacturers reputation, and guarantee is what you have to go by.
Jack