Class allocation in the academia; are we doing it the wrong way?

I've been working in a handful of universities for a number of years and in all of them, I've noticed one thing very common; that is, that the allocation of classes are done giving the Lecturers the most teaching hours and the Professors the least. 

I've always wondered, and in the end, inquired about it, only to be informed that the Professors, who without exception have PhDs and scores of research papers to their name, need more time to 'research', hence are left in peace and with less number of teaching commitments, whereas lecturers who require as a condition of the job to research and publish articles in order to be promoted, are given full load of classes.  

If this is not a complete and erroneous swap of responsibilities, then what is I am unaware. 

Any comments on this?

Life of a university lecturer

As we all know, a lecturer is expected to do research in his field. It's not like any other profession where you just carry out your duties in office and the rest of the time is to yourself. If you work in the university, you have to indulge yourself into research and it is expected that research be one of your main profession.

So it's not a job of a university lecturer to lecture in classrooms and come back home having the entire evening to himself. He is supposed to do research to further his discipline.

A lecturer generally takes 16 to 20 hours a week teaching, along with the preparation needed to teach. On top of that he goes through the entire process of researching. Needless to say, he also has to take care of his persona, social, familial and spiritual lives. So, in short he's bogged down, with commitments.

On the other hand, a professor, having ideally completed his PhD and researches, has more free time as he has less teaching hours. He's at the fag end of his career and life. He has few new things to offer.