Christianity is an easy religion to get into since it demands so little from its followers. No other religion is that way. There is always some required level of commitment. Remember the historical context of those times. Desperate times call for desperate measures.
Ideology tends to transcend the methods used to advance it.
They weren't trying to overthrow Rome. Of course not. Nobody and no army of the time had the power to even conceive of such a thing. However, it was possible to extricate one's self from under their rule and gain freedom. I suggest you follow this reasoning a bit farther.