I also never had any issues expressing, and didn't have any supply issues even when latch was rubbish and painful, in fact I tended towards oversupply and had to be careful not to overpump. Even though I didn't struggle with breastfeeding, I rarely bothered and certainly not in the early days as wanted to avoid messing up supply/causing nipple confusion.
With my first, I expressed lots of milk as was going back to work at 6 months, but she rejected the bottle and would only drink from a cup, so we gave up. With my second I didn't even bother trying to express and get her on a bottle as we had no reason to, as I wasn't going back to work till 9 months. I've never been that bothered about not being able to leave the baby in the first few months though, and generally found after that if I bf baby before I went somewhere I could pop out for a bit anyway. This time I am going back to work at 7 months so will try to make more of an effort to express and get baby to take bottle, but if it doesn't work out then it'll be fine in the end - it was with my eldest.
I think the main reason to potentially avoid expressing and bottle feeding in the first 6 weeks is as @MamaFirst says, it can lead to nipple confusion and baby rejecting the breast (though experiences vary). A friend of mine had a baby a few months ago with severe tongue tie and was told to top up with formula and expressed milk, and she had a struggle with him rejecting the breast because it wasn't as easy as the bottle. I have heard about paced bottle feeding which might be something to consider for those who are planning to combi feed or regularly feed expressed milk feeds. No idea how it works but it is supposed to help with avoiding bottle preference (I think?).
On the feeding in public thing, I think each to their own but I never had a problem with doing it and never faced any comments or negativity about it. Its just feeding your baby like someone bottle feeding a baby and I found most of the time people didn't even notice I was feeding.