I personally approve of SBMM, but there is one argument that I have seen that I do sympathize with some. Basically, that when you play a competitive game without SBMM then you get rewarded for your growth in skill by increased wins and easier matches. One might start off really struggling, maybe only winning 10% of their games, but if they keep practicing and putting in the effort they will start to win more and more, perhaps eventually winning 90% of their games. This adds a tangible feeling of progress. It's like being max level in an RPG and then going back to the starting area and one shotting the mobs. You can see how far you came. Meanwhile, with SBMM, you will often end up with a winrate around 50% no matter how good you get. In fact, you get rewarded for success by getting harder matches.

Now, the major question is if that experience, which likely does feel very rewarding for certain players, is worth the downsides of new players getting utterly clobbered while veterans get to chill out as basically perpetual smurfs.