but bitcoin has weaknesses. you can't deny that. the main weakness being that it is not backed up by something like gold. gold could then be used to measure the value of bitcoin. and gold has real world use.
Even gold isn't backed up by anything, right? 
So why do people trust it and want to pay with expensive value? Because people believe Gold is valuable. The main thing here is people's trust. It is the same as Bitcoin, it doesn't need to be backed up by something because people trust it. People believe Bitcoin is something valuable and useful for human life. In this matter, something like Gold and Bitcoin is acceptable although it is not guaranteed by anything.