Microtransactions are bad, mkey?
The main reason is that they cause bad game design. It can be best seen when the game has a progression system and there are microtransactions to progress faster. The developer has a financial interest in making a game that encourages buying microtransactions, so they add grind and allow paying to skip it.
Here it is worth noting that I understand grind as a purely negative word. It is an overly tedious progression and no amount is acceptable.
Moving on, my good friend once said: "Grind is content. Why would I pay to not play the game?" And he was right. Developers are charging you for not playing the game and made parts of it bad so you are more willing to pay.
For me, the only acceptable microtransactions are purely cosmetic ones, obtainable only for money. Unless we talk about single player games, where no microtransactions are acceptable, because you are paying second time for content that is already there and no other service is provided, like running servers (sometimes DLCs come very close to this).
There is also a special kind of microtransaction that gives random reward, better known as loot boxes. These can trigger gambling addiction, essentially scamming ill people. Most people find that sickening but even if you don't, do you want the likes of EA be the ones to rake all that money?
So, what is the alternative. In case of single player games, just a single payment, like we always did it. In case of multiplayer games, I am a fan of monthly payment. With it, there still can be free players but they would just not have access to everything. And if you are willing to risk it, you can try supporting the game through donations or voluntary hosting.