[cbhl]

Users can turn on "showdead", which will allow them to see all comments (and upvote them, if necessary).

In general, disagreeing is just fine; one can do so in a polite way. Being a 'jerk' usually entails disagreeing and being vitriolic about it. (An example of this is insulting the person rather than addressing why one disagrees with the arguments in the comment itself.)

[jaredsohn]

There is no karma requirement for 'showdead'; it just requires being logged into an account.

[cbhl]

Thank you, I have corrected my original post.