I have visited the Spanish Steps many times. I have even sat on them once or twice. Just sitting on the steps is not the same as eating or lounging or brewing coffee on them (as happened recently on the Rialto Bridge in Venice).
The last time I was there, people were covering the steps as if they were the bleacher seats in a stadium. It was too much, IMO. As long as people are off to the side and not blocking the ability of others to move up and down, I am not sure I have a real problem with it.
The problem with much of Rome (and Venice and Florence and many other cities) is that the number of tourists has increased significantly, but there are few free places to sit down and rest on an actual seat anywhere when touring around the city. If they want to keep the tourism dollars rolling in they need to limit policing to the more extreme cases, IMO, or provide more seating.
Yes, it is important to show respect for ancient monuments, but there needs to be some balance or common sense on both sides. We love to stop at a cafe, but not everyone can afford to do that.