You don't have to actually fly to know about the liquids rule. It's been on the news, quite a lot. People talk about it, there are numerous posts about it on here.
All the airlines have different rules re bags etc and they sometimes change, so if you haven't flown on that airline within the last couple of months, it's a good idea to spend a few minutes reading the information on their website, so there's no nasty surprises when you get to the airport.
So why make all the fuss about liquids when they were going to take the luggage off them and put it in the hold anyway
They don't know that's going to happen - most bags go in the cabin.
Or people can take the liquids out of the bag and put them in their pockets, or after security, they can collect up all the little bottles and combine them together in a bigger bottle. You can buy a handy sized one in the shop after security. You know, the big glass ones full of flammable liquids
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Airport security often doesn't make sense. Trained killers will be able to cause mayhem with all manner of household objects that are not banned from flights anyway, while the vast majority of us have no desire to do anything of the sort, and wouldn't know how to anyway.
But rules are rules, and if you want to fly, you need to follow them.