Well, if you think that it would be more reasonable and expedient to require users to read a contract beforehand and then authenticate themselves to the service

Well, if you think that it would be more reasonable and expedient to require users to read a contract beforehand and then authenticate themselves to the service before accessing any content―please, knock yourself out on your site. It appears that the rest of the web gets by pretty well using the legal framework I've described. Because, you know, they tend to choose things to be pragmatical instead of those that “can be done.”