While i appreciate you wanting to look out for invisilibysyndrome's plants, you are wrong
If you disagree i'd be interested to see where you got your information from.
I am not "Wrong" Mr. Rake, I am being cautious since I do not know the specifics of the environment where the cactus live, in ground, or in pots, and my advice will gently boost the growth without the risk of over feeding.
Proper soil for cactus is organic poor, and mostly inorganic material.
If you know what you are doing, you can use a higher nitrogen ratio (7-10) in a very diluted form, early in the growing season only. Organic ferts like worm castings are also reasonably safe in light application. I will give you that.
However, your statement of "any old fertilizer" leaves no restrictions, or additional cautions. So you think I could use my "Super grow, 15 -20- 30 full strength on my peyote's? Maybe pour steer manure on the top 2 inches?
Unlike you, I will take full responsibility for any and all of my advice, as I do care about the well being of all the members plants, and I have been growing cactus for over 40 years and made quite a few mistakes along the way. I give advice based on my personal experience and accumulated knowledge, with the benefit of not wanting anyone repeating what I have learned had poor or catastrophic results.
Do you personally grow cactus (with any success) or have any concern for the repercussions of what you advise? Is the commentary here based on experience, or are you as well doing a regurgitation of read material with no hands on trial? As you yourself stated,
"Internet pages all do advise low nitrogen i agree, but this is just baseless copy paste"
Why do you consider this "Baseless" ? You ask me to quote sources, does my own experience count?
I do, very much care to see people here, including you, be successful with their grows.
Using a higher nitrogen content is quick burst, followed by a crash and vulnerability. Cactus in their native environments have low organic content in the soil, and nitrogen poor soil. As a result, they are for the most part slower growers, yet able to withstand long periods of stress. I will agree that someone with experience can use a higher nitrogen fert on cactus if it is properly diluted and used only with a set of safe parameters, and some very specific circumstances.
My intent here Mr. Rake, is not to be belittling, but to point out the need for far more elaboration than what you provided, and an attitude of personal investment in the results of any advice you care to share.
Here is some interesting reading on nitrogen and cactus