If this is the way to put the question under discussion, you are surely correct. If all films = ice cream, and what we see = flavor, then there is no point in comparing one film with another and discriminating among them. If the comparisons of the varying grounds for evaluating them are related to the taste buds they excite, there is some point in making this known but it's still basically futile.
The question is whether Jail Bait is one flavor and The Asphalt Jungle another flavor. Both are ice cream, it can be agreed. Both a jalopy and a classic car are automobiles too. Are they only different flavors?
Certainly, both have a realm of enjoyment. Both can be tasted for different pleasures or grounds. That too can be agreed.
Does that mean that one cannot on some grounds be judged better than another or superior to it? Does every judgment resolve into a matter of taste?
Maybe there are degrees of taste. There is good taste and bad taste. Vanilla can be top-notch or artificial. Chocolate can be rich or diluted. Wines have different flavors. One cannot discriminate among them if one judges them by personal preference because different people have different preferences, but one can tell them apart by other ways. Imagine that a refined palette may be replicated by a scientific decomposition of the food or drink. Clearly this cannot be done without criteria. With films, the discrimination is much more difficult, and we find critics disagreeing as they make their judgments about quality. Scientific scales are not in general use among them.
RichardW didn't make a complete case against Jail Bait. (I've never seen it myself. I introduced a few remarks about The Violent Years from a few years back.) He did observe "They're so bad I can't watch them...Ineptitude and infantile-ism are not things to celebrate." Here two criteria of goodness are being invoked. One is the capacity to engage the audience to see the story all the way through. The other is skill in telling the story. These may or may not be useful criteria of refined taste, but at least he put them out there to be discussed. I didn't see anyone addressing what he said.
He also observed "They're so bad I don't understand how anybody can watch them. And yet they sell on home video and they sell tickets in repertory theaters. His appeal mystifies me." The subsequent comments seemed to tell him that he shouldn't be concerned about what's good or bad and that any appeal is equivalent to any other appeal. This is not a satisfactory response, in my opinion. It's nihilistic. Human beings go to great lengths to dispel nihilism even if we cannot prove either its uselessness or its negative effects.
I too find that a bad film fails to engage me. But clearly there's an audience for pictures that I and RichardW and you don't find engaging. So, can this criterion be made to discriminate between bad and good films or not? I submit that some bad pictures become objects of ridicule or laughter or are called camp or objects of concentrated badness and that the pleasures of the audience then derive from quite different sources than when we become emotionally involved in other films that we take seriously. Most people do not take Jail Bait seriously, it seems. A picture meant to be serious becomes an object for jeering laughter. This is an implicit judgment that it has not attained some other artistic criteria.