I'm curious for an example of both a setting/situation as well as one of the comments/compliments you give. It's hard to judge otherwise, but I think, at least personally, there are very few contexts in which I'd consider it wise/comments I would feel comfortable making without it feeling wrong (as you suggested).
I cohabitate with a living example (my life partner) of a person with breasts so large that I would notice them on the street as a stranger. She tends to get catcalled when she visits more conservative, "country life"-type areas in California's somewhat cancerous central valley. But it never happens in our more liberal area.
I simply can't separate the body of a complete stranger, regardless of how much I might be thinking about it sexually, from their humanity. I know I hate unwarranted discussion about my own body, and I'm empathetic to a fault. Myself, I personally ascribe almost no value to compliments I receive regarding things that I have little to no control over (such as hair color, eye color, unplanned weight loss, the size of my sexual organs, etc.), but I greatly value compliments to things I have committed myself to improving (such as my cooking/writing/piano-playing, a toned physique I achieved with exercise, etc.)
I would imagine there are very few compliments that most random busty women going about their lives in a public setting are going to truly appreciate, especially if it's a context in which they'r likely to feel trapped/captive - such as they're at work, they're on public transit, they're walking somewhere and being approached on a much faster mode of transport like a car or a bike.
I'd err on the side of keeping all that in mind if I was going to try and take your approach. I don't think you're a terrible person as you say, and I completely understand the urge to do what you're doing (because I often go wild in telling a buddy in the car next to me just how gawd dayum BIG and PHAT the ass or tits on the girl we just passed was), but I'd be hard pressed to think of a situation where I'd approach a random busty woman and make lewd remarks. Maybe this makes me a ninny poopoo-pants pansy or something, but I try to always remain cognizant of the human being the boobs and butt are attached to.