i'm probably going to be the odd one out. i do agree to a certain extent with your dh amila.
there are some things that i choose not to buy from thrift stores because they are not in abundance. wooden toys for example. i usually see the plastic ones in abundance but not the wooden ones and i will purposely walk past them because i know we can afford to buy them brand new. i always think that there might be someone who only has a toy budget of say $10 and would also love some wooden toys for thier child. just because you are low income doesn't mean your children deserve any less you know? and well i'd feel bad if i stripped the hypothetical child of that wooden toy because even though i could clearly afford the extra $20, i just refused to spend it. even though the salvation army needs money to support thier charitable efforts, a good amount of the salvation army stuff is also purchased by low income earners. they may not be low income enough to qualify for money/coupon assistance from the salvation army themselves or other charities, but thanks to the low prices at the thrift store, they can still have some benefits. i am sure there are many low income mamas here who are thrilled when they find a really nice purchase for thier children for cheap. it's those people i hope to leave the nice, hard to come by stuff for. in our case, the nice, hard to come by stuff are wooden toys and good books.
clothes i don't feel bad about buying. there is always a huge influx and often more than they can handle. same with furniture and homewares. toys and books for some reason are not in abundance at our local goodwill stores and so i refuse to take what little there is.
i also regularly donate and have donated many items brand new or hardly used. the salvation army really helped our family when i was growing up, i am forever indebted to them... i have been on both sides (being able to afford and not being able to afford) and i know it would have not been very fair if people who could afford more took all the nicer things simply because they refused to pay more, and we were left with all the cruddy stuff to purchase. again it depends on your income, how often the stuff is replenished and whether it is in abundance. these rules i have are based on my current situation - i am by no means implying that this is for everyone.