Why did Southerners believe preventing the expansion of slavery was an attack on their way of life?

Defenders of slavery argued that the sudden end to the slave economy would have had a profound and killing economic impact in the South where reliance on slave labor was the foundation of their economy. ... The cotton economy would collapse. The tobacco crop would dry in the fields.

Explanation:

the enslaved people onboard suffered from illness with some frequency

b) the confederacy had to pay all union war expenses.