In itself, being in the rubiaceae family doesn't mean jack shit. Fourth largest plant family in the world that contains stuff used to make dyes, ayahuasca, and ipecac. Several plants in the family contain phytotoxins. Others have a symbiotic relationship with a bacteria so powerful, that it has been known to kill wild animals. Do not use its relation to coffee as something used to show it is safe, because it doesn't.

Just look at Solanaceae, which contains tobacco, potatoes, bell peppers, tomatoes, datura, mandrake, belladona, gooseberry, and eggplants. As you can see, there is a wide variety of plants that can exist within a taxonomic family. From

There are many reasons kratom is safe, but this is not one of them. It is such a different plant to coffee, you can't really compare the two to any significant extent. Even within the Mitragyna genus, the trees can be so different. Parvifolia contains isorhynchophylline, which can result in inreased autophagy and has been linked to Parkinsons. A compound that I must stress, mitragyna speciosa does not contain.