The reason that rescues require dogs to live indoors is because the way the majority of outside only dogs live is not suitable by any means! That's also why it is illegal in many places nowadays. Pretty much the only way I see that being okay is in cases of working farm/livestock/farm guard dogs who have adequate shelter, heat in the cold and air conditioning in the heat. Outdoor kennels are another thing but as far as a family companion dogs go it is not okay for them to live outdoors. Even if they spend the majority of the day outside typically they still need to be able to come inside in extreme weather conditions and to sleep at night. (But dogs do need a certain amount of outdoor time for their physical and mental wellbeing.)
All too often dogs get tied to a dog house or worse, a tree and left to fend for themselves other someone bringing them food and water (hopefully). That's why these rules are necessary.
Also seeing as most dogs LIVE for their human family naturally they would want to be with you and would of course feel left out and neglected if they were left outside while the rest of the family is indoors! The positive effects of them being inside around people are endless! They require mental and physical stimulation and socialization just living with and being with people that they don't get outside by themselves.
It seems you must have some interest in dog training to some extent since you're here so from a training standpoint your dog should be in a controlled atmosphere at least some of the time to learn and develope social skills and some good structure among countless other things and when left to their own devices outside they're going to have all the time in the world to decide for themselves how they should conduct themselves in life. They must be consistantly guided in order to learn how they need to act and you won't be able to do that from in the house with them outside.
Learning to be alone should be only a small part of their life. Please keep your pets inside!