It has been marketed in shampoo to treat children for head lice. It is used regularly in urban areas for mosquito control. Malathion has a record of safe and effective use in past exotic pest eradication programs in Florida and California. I've heard it is highly toxic and dangerous to use. Toxicity is dose related.
Safety pertains to how one handles a material.
Even highly hazardous materials can be used safely. Malathion is not particularly dangerous or hazardous to use. Relatively large doses are necessary for it to be toxic to humans or other animals. The small amount of malathion people might come in contact with as it is applied, is well below what is known to be toxic for humans. Concentrated solutions of malathion are sold for use by home gardeners in many neighborhood stores that carry gardening supplies.