Memes

Neither of those are what leftists say. Capitalism doesn't work because of the structure itself, you have problems like the Tendency for the Rate of Profit to Fall, and the inherent exploitation within. You cannot have Capitalism without exploitation, and you can't have Capitalism with democratization of production, even if you had a perfectly selfless Capitalist, it still wouldn't be democratic and would still have the same structural issues.

Similarly, Communism isn't "people working for the common good," it's people working to improve their own material conditions. Just because production is democratized doesn't mean it depends on people working for absolutely no reason.

There are non-strawman arguments you could make, but this ain't it.

"Capitalism does not work because people are selfish, and selfish people are incentivized to harm their fellow man by capitalist structures. Under socialism, selfish people will work toward the common good because working toward the common good is the easiest way to earn recognition and status"

"People are selfish, and it is in 99 percent of peoples self interest to overthrow capitalism in order to improve their material conditions"