Big dog bites = P.T.S, Little dog bites = Nothing?

Okay...At the boarding kennels where i work we also have a 10 kennel rescue for RSPCA dogs waiting to be re homed. Last week a Chihuahua came in from another rescue as he was with 2 bltches that had come into season so they needed to be separated. For the first few days he didn't come out of his cage, now he will. He is VERY selective at who he likes and dislikes. He doesn't let anyone at work put his lead on apart from me. He will growl at other people and constantly bark at them aggressively (hackles up etc). Today he bit an employee in the morning when he was trying to get the lead on as someone had come to look at him (potentially re home). I then managed to do it as he comes and allows me to put the lead on him. The people spent nearly 2 hours with him and finally decided they wanted him but we needed his vaccinations done which we are licensed to do ourselves. (He was allowed to go then and there because the people had recently adopted another dog from the shelter 3 months earlier)...We took him to get vaccinated in the shed. There was 3 of us trying to restrain this tiny Chi...he barked, growled and bit!! He wiggled and squirmed his way out of hands, towels, dog gloves etc!! He needed to be muzzled before we vaccinated but there was no chance. During all this he bit another employee while she was wearing dog gloves - which dogs aren't meant to be able to bite through.. he then bit the boss 5-6 times all over her hands. We refused to let him go to his new home as his shots hadn't been done but tbh he wasn't really in a fit state to go that day anyway due to his outburst of aggression! Getting to my point...there is now discussion whether to put him down or not??....They are actually considering leaving this potential dangerous dog to live and be re homed coming up with the solution of getting him neutered, but then, the vet still won't be able to get anywhere near him to give him the sedative. Because it's a chi, and because he's so small he is getting away with very bad behaviour, if he was slightly bigger, say a JRT, then after his 3rd bite he'd be put to sleep, if he was a Border collie then after the 1st bite he'd be put to sleep, if he was a Rottweiler then the first sign of a potential bite would result in him being put to sleep!!! Surely he can't be re homed?? I dread to think what would happen if a little child got anywhere near him... Why are the consequences of biting people different for a big dog and a smaller one?? - They both have the potential to cause a huge amount of damage..!!