Will most people go the three lower dimensions (hell, animal womb, ghost realm)? "In the same way, monks, few are the beings who, on passing away from the human realm, are reborn among devas. Far more are the beings who, on passing away from the human realm, are reborn in hell... in the animal womb... in the domain of the hungry ghosts." (Pansu Sutta, SN 56.102)

According to this quote most humans go to the lower realms. This doesn’t make sense to me because majority of humans though imperfect are ethical and moral. How true is this? How strict should we live our lives so that we can be reborn to a higher dimension?
In Buddhism, the 'human' realm does not always refer to something biological. The word 'human' ('manussa') in the Pali language means 'high minded'. For example, AN 6.39 says:


  Bhikkhus, a god, a human or any other good state would not be evident
  from actions born of greed, hate and delusion. Yet, bhikkhus, from
  actions born of greed, hate and delusion a hellish being, an animal
  birth a ghostly birth or some other bad state would be evident.


It appears the Pansu Suttas SN 56.102-131 are about what happens when the Four Noble Truths are realised and when the Four Noble Truths are not realised. The sutta quoted in the question is only an excerpt. The complete sutta is:


  Few are the beings who, on passing away from the human realm, are
  reborn among devas. Far more are the beings who, on passing away from
  the human realm, are reborn in hell... in the animal womb... in the
  domain of the hungry ghosts
  
  Why is that? 
  
  It’s because they haven’t seen the four noble truths. 
  
  https://suttacentral.net/sn56.131/en/sujato


The message of the Pansu Suttas appears the same as the message of the Lonaphala Sutta. The message of the Pansu Suttas appears to be when a non-Arahant enlightened person who has realised the Four Noble Truths falls away (cutā) from being human, such as if they are unmindful and perform an unmindful skillful action, due to realising the Four Noble Truths, they won't fall into the lower realms because they realise there is no self that did the unmindful unskilful action. Instead, they know the doer of the unskilful action was the element of ignorance. Therefore, their human status/coming-to-be (paccājāyanti) is not lost. 

The Pansu Suttas can be contrasted with ordinary suttas about kamma, which are about the ordinary outcomes that follow from (upapajjati) various acts of kamma (actions). 

It is important to note, in the ordinary suttas about kamma, proceeding to (upapajjati) 'heaven' ('a happy state') due to a skilful action is not permanent. 'Heaven' is not permanent in Buddhism. 

In summary: 


The Pansu Suttas SN 56.102-131 appear to be about, due to realising the Four Noble Truths, how the human or godly state (paccājāyanti) does not change significantly despite unmindfully falling away temporarily from that state. 
The ordinary suttas about ordinary kamma are about  the ordinary outcomes that follow from (upapajjati) various acts of kamma (actions). 


Note: The word two Pali words 'paccājāyanti' &amp; 'upapajjati' commonly translated as 'reborn' are different. The word 'upapajjati' means 'to proceed closely to the former' (for example, from performing an action causing pain, one proceeds to a painful state). The 'paccājāyanti' appears to refer to the attainment of a realm status.