"We've tamed the beast" is an excuse for sexist behaviour which takes the form of explaining that while a serial harasser or abuser may behave badly in other communities or spaces, he is well-behaved in one's own community and does not comprise a reason for women or others to avoid a community.
The reasons for the belief that a known serial abuser is not going to reenact this pattern in one's own community might include:
- the presence of anti-harassment norms and enforcement
- good personal relationships between the serial abuser and community leaders
- inability to believe that someone with attractive personalities traits or who is good to you personally can be abusive
- lack of reports of abuse within this particular community (falsely extrapolated to a belief that therefore there has been no such abuse)
- expressions of contrition on the part of the abuser for past acts
- disbelief in accounts of abuse in other communities, especially if, eg, the actions were not illegal or were not brought to the attention of law enforcement or did not result in a criminal conviction
- a belief that people should be entitled to a "fresh start" when joining new communities
- pride in the community's inclusiveness
- pride in the community's ability to reform/educate a serial abuser
- various possible explanations for abusive behaviour elsewhere, eg He's just a troll
However, it is not reasonable to ask that geek women trust your community's ability to tame the beast, and allowing a serial abuser to remain part of your space will inevitably lead to people who fear him or what his presence means about your norms refusing to join your community. In addition, it is easy for serial harassers and abusers (who may well be exceptionally socially skilled) to exploit the above beliefs on the part of the community as part of grooming it to allow and excuse their usual behaviour patterns, or to justify their inclusion in yet other communities.