That is what I do too. I guess though it has two factors:
1.) Comics can be sorted by rating, which means the worst ratings will have the worst chance of getting a good (and possibly objective) aknowledgement.
2.) Psychologicaly comics with worse ratings might loose potential readers. Of course everyone should make his or her own mind, but not everbody does that. I don't know about webtoons itself but I bet there are some scientific papers who research those psychologic consequences (I will not search for them though since it is boring work. ^^)
So basically what I am saying is: Good rating --> More people will look at it. Bad rating --> People are already biased and might not look, since others did the "job" for them and disliked or downrated it already.
I myself prefer a "like"-System. If you like it: Like it! If you don't: Move along and don't make a fuss about it. lol That probably was the best thing facebook had, but they screwed that over, so eh...