I agree and disagre at the same time. Whatever art speeks to a person is certainly valid in that respect and i would not want to denigrate it( at least not to virantly) but at some point lack of organized tonal variations if you will crosses the line into an objective lessening of musical quality beyond mere taste. ( at least in my opinion)Drawing a line where that point is was what i was referring to as being blurred.There is alot of music I dont personally care for but i recognize is good ie well written but don't see that in alot of the newer popular music( I'm always thinking I can't make out an actual tune hear just sounds). Your point however is well taken that with art of any kind if it works for someone then its good for them at least.
But see you just said: "At least in my opinion".
And that would be correct.
We can argue facts with planes all day long, but no one (myself included) can present opinions as fact. And that is why there is no such thing as actual bad music. What is good or bad is your opinion.
I hate rap music, yet it has what you describe as good rhythm and melody. To me it still is not good music. It is my opinion.