A campsite that doesn't cost an arm and a leg to stay at, like a municipal one and get the local police to collect the money from whomever is staying there. You achieve income and you also proactively police the area. Make it a tent only campsite and maybe require a credencial to stay there. It doesn't have to be in the middle of the city either, just needs to be affordable for those pilgrims that aren't well off enough to afford albergues or have conditions that don't allow for them to stay indoors (health, ex-military, etc). Priced to be inclusive of all and you will remove the vast majority of the people camping in parks and anywhere they feel like. FTR, the campsite near the Carrefour is pretty expensive.
I stayed on the As Cancelas campground up on the hill last year. It cost about as much as a private albergue. If I recall correctly it was possible to check in until midnight. Supermarket more or less next door. Perfect after a long walking day and for staying a few days after arrival in Santiago. They even have a pool ect., I'd say the price is okay, shade in the parcelas, not too far from the cathedral... I had worse campsites for more money elsewhere.
And why would you need police to run a campsite? The police has other things to do, namely their work. They're highly trained professionals. People with tents are not more criminals than those in albergues. Or should the police Run the albergues, too? I'm not sure they'd be happy about that!
Honestly, I'd love a cheap, simple campsite in Santiago as much as anywhere. But tent campers are such a tiny fraction of visitors to Santiago that there's probably not much public interest in something like that.
Easiest option would be to officially allow camping for a small fee at the Monte do Gozo albergue. But I think that's unlikely, because there's a campsite closeby (even though it is not cheap, no food shops nearby, bar closed in the evening, so more or less useless for pilgrims on a budget, who probably simply discretely wild camp close to the albergue, setting up tent in the dark and leaving before sunrise, so unnoticed by anyone).
Disrespectful people would still camp in a park next to the cathedral, even if there would be a free campground outside the city center, because they don't give a sh*** and do what's most convenient for them.
The problem of people doing wild camping in a totally inappropriate way has nothing to do with people on a budget or with people who prefer to camp. It's just idiots who happen to carry a tent.
Other idiots who stay in hotels might be the ones who have a fancy picnic in the plaza to take some photos for Instagram with their Champagne, or someone staying in an albergue is the jerk who writes their name on all waymarkers and steals the km plates.
I think the number of people behaving disrespectful and inappropriately is high simply because of the high numbers of people visiting Santiago. The more people come, the higher the number of jerks and idiots.
The tax (where I live it's usually 2-5€/day in towns with many tourists) can help maintaining infrastructure for tourists or to pay for expenses like waste disposal (many visitors, more rubbish), ect.
It does not stop entitled people from acting selfish, nor idiots from acting stupid.
And please don't throw all tent campers into a category that requires police supervision of the tent area. Most avid tent campers / hikers are extremely respectful to their surroundings and the environment.