I never said they are easy, I admitted that I have no idea how hard the honours and masters degrees are. But had I do know for a fact is that the undergrad degree is easy to get into and they tend to attract the "party animal" students looking to just breeze through university. These are the same people that one day may go on to post grad psychology.
It's also not as rigorous as the "hard" sciences.
That's where the perception comes from. All these factors affect the perception of the field, accurately or not.
If they do honours and masters in psychology then they have clearly transitioned from someone looking to 'breeze their way through university' into someone that has an interest in the field.
I highly doubt some person who just wants an easy degree is going to go on to become a clinical psychologist without changing their perceptions/outlook, or just for the sake of it.
I can apply what you are saying about the people to many other fields. The truth is you are going to get people who are good and bad at their jobs in any field, be it psychology, engineering etc.