A lot of people adopt animals (especially kittens or rabbits) because they think they're cute, then get tired of the animals when they grow up or when they're too much work to care for. I assume the shelter is trying to discourage impulse adoptions so that the animals they adopt out don't end up coming right back. The adoption fee also helps cover the cost of up-to-date vaccinations, spay/neuter surgery, and a microchip.
I concur with the last statement, having volunteered at the Humane Society in both Franklin and Delaware counties. Paying for the pet shows commitment to further expenses and treatment needed regularly. It also covers the cost of spay/neuter/regular vaccinations given the pet to make it adoptable and safe for the people adopting, not just the pet.
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