There are actually a lot of rules to magic.
Like yes, there's no rules, but if your takeaway from that is that there's literally no rules, then I think you missed the larger conversation about the specific ways in which there are no rules.
What "there's no rules" means is that there is not one universal set of rules that applies to every practitioner.
It means that nobody gets to act as an authority on what the rules are for everyone else.
It means that if you show up on somebody else's post saying "the first rule of witchcraft is that you must only use magic for good" you will probably (and deservedly) be told to fuck off.
What "there's no rules" does NOT mean is that there are literally no rules. There are SO many rules. People just work within their own set of rules.
Some rules come with the territory of working within a specific tradition.
Some rules are set by entities that practitioners work with, and might be quite specific to each individual.
Some rules are like laws of physics. They define the mechanisms by which magic works within a paradigm, and what the limits are on what it can do. A magical practice consisting of "I can do literally anything," is typically a practice that hasn't had a lot of genuine thought put into it. I have yet to meet anybody who can literally turn invisible or fly.
Some rules are more like a personal code of ethics.
So, when you burst into someone else's post to announce that there are no rules, you might not be told to fuck off quite as quickly as if you turned up to impose your personal rules on other people, but you are essentially signaling that you do not understand the concept of rules within a magical practice.
Disclaimer: some people are going to be obnoxious and make their own posts about how everyone else should be following their rules, and while it might be tempting to correct them, in my experience these people tend to get 0 notes, and you're more likely to give them the exposure they desire by starting a flame war. When they find that followers don't come flocking to them, they eventually get bored and give up.