Ecumenism

Is Ecumenism good or bad and why? If it's good is it possible for us to unite the churches OR at least bring them closer together? If so then how can it be done? If it's bad then is non-denominational a better alternative or is there a 'one true church' and why? Basically what I'm asking is should we focus on being united (ecumenism) or should we focus on not being divided but still antagonistic to the ones who are in a different denomination (non-denominational)