Reading a sentence that starts with "I mean, ..." makes my whole body shudder. As verbal filler, it straddles the acceptable, but as a writing tic it is totally useless and occupies the same lexical waste heap as any other junk phrase meant to approximate the cadence or tone of regular speech. If I am bothering to read something you've written at all, I already carry the assumption that 1) you really do mean everything that's been put down, and 2) in the exceptional case that you don't, the context is sufficient to see that it's sarcasm. Any other scenario must either be intentional misinformation or a failure to communicate.