Let's first lay out my basic view... I loathe microtransactions.
I'm not an anti-industry activist, and I don't have a serious bone to pick with any individual company about them. I've had a few bad experiences with them, but the reason for my loathing is something more fundamental, that I came to realize only after I'd put a year or so between my worst experience with them.
First of all, my experience was with an MMORPG on PC, rather than a blockbuster title or a smartphone game. As such, in some ways my experience is probably the most 'traditional' one for the original form microtransactions took... the 'pay-to-win' model of massively multiplayer games.
Basically, in that game, you could not only buy clothing and armor with real money, you could also massively accelerate your experience gaining and basically not even do several annoying but important quests that gained you new skills and and access to higher classes if you were willing to fork over enough money. Now, this was the game that essentially put an end to me playing MMO's, even out of curiosity. Before then, I'd only played subscription-model games, and as a result, I'd never experienced a game designed to essentially squeeze more and more money out of people in that manner. My frustration kept growing, because up until then, I'd basically played games when they first came out until I reached the level cap, then dropped them, cancelling my subscriptions and deleting my account. However, in that game, I kept on running into roadblocks to my curiosity about the world I'd entered, and when that frustration reached its peak... I made the mistake of indulging in microtransactions to speed things along.
I probably wouldn't have realized what it was doing to me or my bank account, if it weren't for the fact that I got caught up in a minor scandal where a GM was raiding players' accounts using his administrative rights and selling off their non-bound equipment and items on the marketplace. While it wasn't a direct result of my microtransactions, it nonetheless served to cool my head... and make me realize I'd basically thrown away money on virtual items, some of them with frigging time limits for their use. I got my money back for the stolen items, but only after I flatly stated I wanted nothing to do with the game after that and threatened to lawyer up if they refused. So, I managed to escape before I reached the degree of financial loss Japanese 'kakinhei' have been casually enduring for years before the concept wormed its way over here (incidentally, it is much, much worse in Japan, China, and Korea than it is here...).
Microtransactions are essentially an outgrowth of the dlc concept, save without even attempting to give you value for value. Once you've purchased dlc, it is yours, you can leave it installed without worrying the 'time limit' will run out, and you don't need to feel driven to show off how much money you wasted to people who were just as stupid as you were. However, the most critical difference is that dlc isn't an 'infinite product'. It isn't constructed to draw ever greater amounts of money out of the user and indulging in purchasing dlc or a season pass for a regular game you like isn't nearly as damaging to your wallet or your mental health as microtransactions are.
Edit: To be clear, I see microtransactions as being one of the most fundamentally dishonest types of scam directed at consumers to have cropped up this century. The techniques are well-established, predatory, and poisonous, especially to those too young and inexperienced to realize that money doesn't spray in infinite clouds of green from the cards in their parents' wallet.