The above post brings up a good point, but it is for just this reason that I wear socks just once and then wash them.
The last two summers a typical (Satur)day went like this:
6:30 AM - row - 1:30-2:00 - in socks - drenched with sweat
9:00 AM - ride - usually 100 mi - in socks - drenched with sweat
3:30 PM - mow lawns - usually 4-5 - in socks - drenched with sweat
6:30 PM - eat dinner - want to wear clean, dry socks
So, for me, each activity meant I had to change clothes, and therefore it was easy and preferable to change socks. It may not have any health consequence at all, but I don't like the feeling of putting my feet into shoes (ready to ride for 5-6 hours) that are all sweaty and wet. Maybe they smell, maybe they don't, I don't smell them, but I do know that when I peel my socks off after riding in the heat they don't smell great.
Also, If I wore the same socks for the whole day (or worse - socks from the day before) I would be making the rowing shoes dirtier and smellier than they get already. Then I would be doing the same to my $250 cycling shoes (I want those to last) and then to my outdoor work shoes. It is also a fact that this will foster Athlete's foot.
I generally shower at least twice on a day like this (which my team calls Seven Hour Saturday). Sometimes if it is hot out - three times, so I don't see why you wouldn't reach for a fresh pair of socks when you bring out your rowing uni, or your bib shorts and jersey and helmet, or for most of you ... your running shorts.
So, yes I work out about 10 times a week and do yardwork twice a week, so I need about 20 pairs of socks each week. If you think it is onerous to launder 20 pair of socks each week - it is about the same as 2 shirts or a pair of pants. Not bad for being able to feel confident when you take off your shoes at a girl's house.
Also, I buy my socks at wholesale. They are 4.25 at my team's shop. Not expensive. Even if I couldn't do that you can always buy socks at a sale. If you needed 40 pair (which I do - just for summer) they would store in something just larger than a shoebox. Again, anyone can do this.