Agree. Users tend to forget to add the additional enrollment trigger on marketing email confirmation status. In case they forget it, it is not a legal problem (because marketing emails will not be sent without DOI), however there are other problems involved:
HubSpot will attempt to send the marketing email again and again for (I think) 24 hours on an hourly basis which leads to 24 timeline entries (email could not be sent) if the contact does not click the DOI link. If the contacts do not click the DOI link within 24 hours, they will not receive the marketing email at all.