The counter-argument they would give is that you get to use the site/service, thus, that is your consideration -- of course consideration for both parties has t

The counter-argument they would give is that you get to use the site/service, thus, that is your consideration -- of course consideration for both parties has to be balanced/equivalent. Thus, the "consideration." But contracts also require both parties to explicitly acknowledge them and understand them -- thus e.g. modifying in secret a contract before signing will just offer a cause for invalidation and fraud to be brought up etc. EULAs are hilarious in this respect that it is an open secret that only a few devout users read them or even skim them.