it depends on what their past entailed, some things could be classed as mistakes and therefore should not be used, but somethings like long term abuse of another (long term being more than one incidence) or multiple acts of criminal damage, drink driving....etc., is no longer a mistake and i for one would not wish to get close to someone who abused another in their past! I also believe that any criminal or abusive behaviour which happened in a persons past should be considered and mentioned and lumped in with any new reasons for being up before a judge/jury! too many people have a string of convictions leaving a trail of devestated lives only for them to be dismissed as evidence of a perpertrators continual wrongs. not sure it makes sense what i wrote but the message is that every criminal act you have done should stay with you, the more you do the worse the punishment should be.