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Doesn't mean it's safe.
Doesn't mean it's not. You could cause bodily harm from vigorous use of a dildo or lack of lube but we're not stifling constructive discussion about sex toys or practices like fisting, although they could lead to vaginal or anal prolapse. "No one should try that at home" is a bit much.
People with mechanical expertise who know what they're doing can easily make their own sex machines at home. The FetLife discussion group, and other sources, have instructions for safe, low-powered DIY machines. Commercial products like the Fucksall and Drilldo are simple, modified power tools. If electric motors worry you, other machines are human-powered via a rocking mechanism or foot pedals.
Keep in mind that some of the commercial sex machines, sold for "novelty use" only, are just motors or motorized pistons that don't have additional mechanics to keep torque in check. Potential problems also include overheating and electrical shock; a good machine shouldn't harm the user when it breaks or needs maintenance.