I know nothing about these claims or Altman, but this argument fits the pattern of three commonplace threads that I hope people will notice in these situations:
1) Smearing the attacker: When someone unknown accuses or opposes a powerful public person, a standard response is to smear the accuser's credibility and reputation, creating doubts in onlookers, and causing day-to-day harm and high levels of stress and pressure for the accuser, and even causing danger (threats, doxxing, etc.). Powerful people can control the narrative - through contacts with other powerful people, by buying resources, or just posting on social media to their many followers. Also, powerful people already have a reputation that the accuser has to change, with many invested in believing it (even just as fans). Unknown accusers have no public reputation - often the only thing known is the smears from the powerful public person - and so others can say anything and it will be believable.
2) Mentally disturbed people - even if that part is true - can also be sexually assaulted. In fact, they are often targeted because they are more vulnerable, and you read again and again that accusers tell the vulnerable, 'nobody will believe you'. Let's not make those words true.
3) Sexual assault causes serious mental health issues.