Me: "Goevernments can effectively ban bitcoin, see China for example."
Them: "Bitcoin is like the internet, it will find a way around any obstacle."
Bad example, try torrents or something closer in anology to decentralization
Me: "Bitcoins may be scarce, but there are plenty of cyptocoins with equivalent or better protocols"
Them: "Cryptocoins will die and bitcoin will not."
The very best will likely be used in some situatioins as well. But network effect, first mover effect etc
Also if a country decides to print more money does that devalue my currency in my country?
Me: "Bitcoin is now more prone to theft and fraud than credit cards, see the numbers."
Them: "Bitcoin will be much safer when it matures."
Isn't that logical due to most the thefts, scams etc being because of 0 regulation rather than the bare minimum at least.
Me: "Mining is already concentrated in a few companies, they may form a cartel and become like the bankers."
Them: "It is a free market so that will not happen."
This is agree with you more on, thats why I have my coins already, first movers advantage etc.
Me: "The Satoshi 2009 blockchain already assigns XX% of all the money to a few thousand people."
Them: "Wealth distribution will improve with time."
How many people do you think who mined in 2009,20010, 2011 even 2012 still have all the coins they mined/bought now? Satoshis mined 1 million don't foget.