Owing to a remarkable property of the standard model, a derivation of proton-decay catalysis by monopoles can be given which is independent of the structure of the monopole core. The result is valid for one generation of fermions interacting with an eg=12 monopole in the limit of unbroken weak interactions. It is a consequence of the fact that unification-induced and anomaly-induced proton decay are indistinguishable in this limit. An argument is given why this should still be true for broken weak interactions. An example with baryon-number violation due to the anomaly alone is discussed in detail and is compared with the SU(5) case. In the bosonized versions of these models the B-violating process appears in a different way, but leads to the same final states.