I think its unreasonable - unless it's a budget hotel operating on razor-thin margins. I've stayed in countless hotels over the years, from budget to five-star, and I can barely remember seeing signs threatening guests with a lost key card charge. Most simply absorb it as part of the normal cost of doing business, just like broken glasses, damaged towels, etc. I can understand charging guests who are repeatedly careless or obviously abusing the system, but making every guest liable for a piece of plastic that probably costs a fraction of the fee just feels like nickel-and-diming. It's not the money so much as the optics. A hotel is selling hospitality, and starting an argument over a key card isn't exactly a great advertisement for it. That said, it also depends on the type of hotel and the clientele they're targeting. A backpacker hotel dealing with constant losses has a stronger argument than an upscale property where the occasional missing key card should already be built into the operating costs. Finally - the guest getting aggressive about this is even more absurd - only ayholes react like this. I recall my son dropping a plate restaurant staff hat put right next to him (I didn't have time to move it way) - the staff wanted a 500 baht charge for that breakage - I wasn't happy, called for the owner (of course the staff claimed they didn't have his number, but 500 baht would be deducted from their wages - BS IMO - but either way, I wanted to complain to the owner about this policy / and-or confirm if it was true or not - I was a regular customer, never returned). In this case - sometime businesses here operate in a terribly clumsy manner - just don't return is the only way to deal with these issues - as some will argue heatedly over small amounts which is quite stupid - and so is a person who'll respond with aggression in such circumstances.
