"Why the obsession with bacteria?"
Well for one thing, bacteria causes bad smells!
But for me, it seems obvious that washing at 30 is pretty rancid.
Imagine being stuck in a stuffy office all day wearing a shirt/blouse, the armpits aren't pleasant when you get home, not to mention underwear. All the bacteria that comes from your sweat and around your personal bits transfers onto the clothes.
Then you throw those clothes into your washer on a 30 degree wash. Now, bear in mind that body temperature is 37 degrees, so logically you will need a temperature hotter than that to get rid of the bacteria that have built up on your clothes.
Fair enough, they won't kill you and won't make you sick in such small amounts. But if you're washing everything on 30 - towels, tea towels, dish cloths, underwear etc - all the bacteria that has built up on all those items goes into a nice warm, damp drum and it multiplies in excess. You're creating a bacteria breeding ground within the washer, which then spreads all over the rest of your clothes and cloths etc. It's cross-contaminiation. You might as well come out of the bath and dry yourself with a dirty dishcloth or sleep wrapped up in your own dirty underwear.
Imagine doing that for weeks, even years, on end...how much bacteria will have built up inside your washer? Dirty clothes and other items go in, bacteria multiply, spread across the laundry. Constantly.
This is even more of an issue when using liquid detergents, which have absolutely no antibacterial properties at all. How many threads have we seen on here with Mumsnetters complaining of mouldy/smelly washing machines and the answer is always "ditch the liquids, switch to powders, stop washing at low temps and do regular maintenance washes".
Being perfectly honest, the thought of washing my bedsheets, underwear and towels on 30 degrees makes me feel sick.
I don't imagine 30 degree washing is a problem for day to day clothes - jeans and t-shirts etc. But when you're washing absolutely everything on 30 degrees, it's pretty rank.