Bravo on saying "let’s not be too hard on people who make the occasional its/it’s slip-up". I'd much rather understand (be understood) what some one is saying, than try to correct (be corrected) for such a small thing. English doesn't compile!
English is not a primary language for quite many people around, you know. And
for those it can take significant effort to metally correct the sentence with
misused "its"/"it's". Try thinking about others sometimes.
You misunderstood me - I'm saying that it doesn't matter, and that it's dumb to worry about whether you're writing it's or its
Maybe I wasn't clear: it does matter, because your reader could be non-native with English, and he/she may need to allocate non-zero amount of attention to fix your spelling.