I don't mind the state investing to stimulate low cost air transport (don't count on LH out of BRU for that). Looking at the bigger picture, I consider this to be interesting for the tax payer who can now go on holiday for peanuts.
The purchasing power for those who travel has gone up and those who couldn't travel can now affoard to do so. I don't see any loosers here.
I also feel you're missing out on all the indirect jobs being generated and what about all the extra tourists&other coming into Belgium. I don't know however if the amount of foreign passengers visiting belgium exceeds the amount of Belgiums going away (is there a net tourist inflow due to Charleroi?)