The World of Tanks/Battleships/Warplanes series, are free to play, with progression through experience ( you unlock higher level machines based on xp points you accumulate through playing and success at it), or through paying to go up the ladder faster or unlock special machines. You can play the free version just fine ( a paying user against you doesn't have a serious advantage), and the developers make enough money from the paying users who enjoy the exclusive machines or earning xp faster. Why shouldn't i enjoy a free game i know someone pays for ( and that someone needs me there too, if there aren't adversaries you can't play)?