bad MTX are buffs and items that you could get in the game but takes ridiculous amounts of griding-- this is what stuffty people do. why wait another day for another life in candy crush while a simple click of a button will get you more? it's proven that money means less when you buy it with a card rather than cash. it's exploiting human psyche imo.
i'm with you on this; there are definitely schemes like this that are exploitative and in those cases the microtransactions specifically are the issue
though with other things, i think it's highly context-specific. if a dev implements microtransactions that can somehow give you a gameplay advantage, then i'd consider that a design oversight or flaw rather than it necessarily being an unethical business practice. if a dev fails to appropriately accommodate for their monetization schemes, then that's a larger issue than just the scheme itself. for instance, if dark souls let people with DLC invade people without the same content, that would cause a major balance issue, but the problem wouldn't be the introduction of DLC, it would be a failure of the designers to appropriately accommodate for it. i think it's totally possible to implement non-trivial microtransaction content (like mounts/pets in MMOs) and still have it be acceptable, it's just dependent on how clever the devs are at making sure it doesn't end up breaking the game's design in unexpected places