Not wanting to acquire a horse with strings attached has nothing to do with the quality of the home. I maintain a very high standard of care for my animals and if I cannot provide it, I don't acquire them. I'm happy to discuss how I care for my animals, but I strongly
value my privacy and rights as an owner.
To me, having a rescue inspect my home is comparable to being investigated by the authorities. I take pride in the home I provide, however I don't report myself to animal welfare to make sure. Heck, an animal welfare investigation would actually be preferable to one from a rescue, because they are bound by the applicable laws and can only act if I have violated those laws.
However I've only seen one adoption contract that actually outlined in detail what they considered to be an approved level of care, and that was the BLM. Most contracts are extremely vague, and allow the rescue FAR too much freedom to repossess the animal based on personal opinion.
Outside of animal cruelty laws, the line between abuse and proper care varies from person to person. There are people who consider bits, or shoes, or stalls, or non-parelli training, or parelli training, or sweet feed, or what-have-you, abusive. No rescue can guarantee me that the person inspecting my home is going to see past differences of opinion when deciding if my care is "good enough", and the adoption contract does not protect me. As an added bonus, most rescues do not reimburse for the sunk cost of caring for their horse should they take it back. With tonnes of needy horses available outside of the rescues, there is absolutely zero incentive for me to deal with them, and a huge amount of incentive NOT to.
I'm well aware that most rescues are reasonable, and as countrylove has stated, most do not fully enforce their contracts. However the point is that if it's in the contract, then it is legally binding. As a diligent, caring owner, I want my full rights and full control - under most adoption contracts I am putting myself in a position where a rescue CAN dictate to me how to care for my animals under the threat of repossession without compensation. Just as these rescues claim they can't trust my word that I am a good owner and need these strings attached to protect the animal, I can't trust that they know what a good owner is and refuse to sign away my ownership of the animal.