Because you can't leave a dog for hours on their own? Some dogs are fine with more time alone some aren't. Its more like don't have a dog if you aren't able to prioritise it's wellbeing. But no, obviously that person should instead prioritise what other people want them to do because someone might think it's rude they leave an event early.
Honestly wouldn't bother me if someone needed to leave my event early for any reason, I'd just be glad they made the effort to show up for a bit.
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Maybe you're reading but definitely doesnt sound like you're understanding. It's not treating them as children, it's treating them based on their needs because as others repeatedly stated, dogs shouldn't be left alone for prolonged periods.
Then people complaint about dogs which aren't well behaved and socialised