No one is going to pay me more under UBI than I earn now because I work harder. I already get paid to work hard.
You don't work because it's your responsibility to make the economy function. You work because people give you incentives to do so. UBI just changes the incentives slightly: You can choose whether you want the minimum or whether you want to earn some luxuries.
You can argue about how many people are going to take the latter choice, but it's ludicrous to suggest you would be forced towards it by your "responsibility" to the economy.
>No one is going to pay me more under UBI than I earn now because I work harder.
If lots of people stop working, then those who continue to do so will become a lot more valuable, and companies will have to pay them more as a result.
Your comment is based on misunderstanding of what actually is money. Money is just a claim for some commodity, like resources or work; it's not a commodity in itself. From microeconomic perspective it is interchangeable, but not from the macroeconomic one.
In fact, under UBI, someone may decide to pay you more money exactly because you're willing to work hard. If you really have the choice of not working, you will have to be more incentivized (with money) to actually work.
In reality, UBI is just a different money redistribution scheme (compared to capital investment), nothing changes much for people who work. It won't however make the people who invest and live from rent (capitalists) very happy, because they will get less of the pie to compete for.