The toxins in beans aren't eliminated entirely by cooking.

So first of all the traditional cooking method for beans is being lost in modern cooking practices. Normally you have to soak the beans for about 24 hours before cooking and the cooking should involve several hours of boiling. With canned beans, which are semi-prepared, or via pressure cooking, which is shallow, the toxicity remains high.

Also speaking from my own experience, there's no other food that gives me an acid reflux or diarrhea faster, or that bloats me any worse than beans do.

Speaking of toxins, lectins aren't the only toxins to worry about. Alpha-amylase inhibitors, which are also found in grains, are another. Phytosterols are another.

Also one example of a toxin that cannot be destroyed via cooking is the amino acid canavanine.

Here's some studies on the subject:

1. "Toxicity of kidney bean (Phaseolus vulgaris) in rats: changes in intestinal permeability": https://www.ncbi.nlm.nih.gov/pubmed/4018443

This ones claims that kidney beans make rat intestines leaky, allowing bacteria and toxins to enter the body.

2. "Phytohaemagglutinin inhibits gastric acid but not pepsin secretion in conscious rats.": https://www.ncbi.nlm.nih.gov/pubmed/11595455

This claims that kidney bean lectin phytohemagglutinin (PHA) blocks production of stomach acid. This prevents proper digestion, especially of proteins.

3. "Kidney bean lectin-induced Escherichia coli overgrowth in the small intestine is blocked by GNA, a mannose-specific lectin": https://www.researchgate.net/publication/14973681_Kidney_bea...

This one claims that PHA ingestion “was accompanied by a reversible and PHA dose-dependent overgrowth with E. coli.”

4. "Precocious gut maturation and immune cell expansion by single dose feeding the lectin phytohaemagglutinin to suckling rats": https://www.cambridge.org/core/journals/british-journal-of-n...

This one claims that high doses of PHA disturb the mucus and shorten villi.

5. "Inhibition of starch digestion by α-amylase inhibitor reduces the efficiency of utilization of dietary proteins and lipids and retards the growth of rats": https://www.researchgate.net/publication/15416107_Inhibition...

And I quote: As starch digestion . . . was negligible . . . the cecum was practically blocked by solidified digesta. . . . [A]s the distension was not always sufficient, the [intestine] was occasionally ruptured and the rats had to be killed.

6. "Canavanine-induced longevity in mice may require diets with greater than 15.7% protein": https://www.ncbi.nlm.nih.gov/pmc/articles/PMC554090/

This is related to the amino acid canavanine, the toxin that cannot be destroyed by cooking.

The study claims that cavanine can block the synthesis of nitric oxide, an important vascular, immune, and nervous system molecule, can interfere with ammonia disposal, can prevent reproduction in animals and possibly humans.

7. "Effects of L-canavanine on T cells may explain the induction of systemic lupus erythematosus by alfalfa.": https://www.ncbi.nlm.nih.gov/pubmed/3155617

This study claims that cavanine can induce the autoimmune disease lupus (systemic lupus erythematosus).

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Granted many of these studies have been done on mice, because doing experiments on humans is unethical and expensive and it's pretty obvious that humans aren't mice.

But as you can see, the claim that beans are toxic is anything but laughable ;-)

Also note that the "dose makes the poison". If you're eating beans once or twice per weak, like many of us do, you aren't going to suffer from it. Eat beans daily however and you're probably going to destroy your gut.