Why would anyone think this is OK?

Why would anyone think that it is OK to start off a marriage with a huge lie regarding past betrayal??? I've been reading people's responses to questions regarding cheating, and am specifically perplexed that anyone would think that it is OK for someone to lie to their partner before marriage about having cheated on them, and then have the "lack of character" to deceive their partner into a marriage where they will be lied to everyday of the marriage???? How is this OK???