1 - In a MMO people make multiple characters. Being a vibrant, changing experience, many times they shift between their main character for several reasons. Restricting people to make one character their main is unfeasible and counter to the premises of this game: choice, freedom and exploration/experimentation. PLAY THE WAY YOU LIKE, as was advertised.
2 - For many of the same reasons stated above, people delete characters. Maybe they didn't like their original class choice that much after a while (and a respec won't solve the problem). Maybe they did a mistake in creation they didn't realize till much later. Sometimes people in MMOs even delete their top leveled, top geared characters for their own particular reasons. It's not really anyone's business - the fact is: it happens.
3 - People paid good money for the Imperial Edition because of the extra content and bonuses. The pets are permanent and can be transferred between characters. The gear conversion ability is available to every character on the account. The imperial horse can be purchased with every character. Why is the Pledge of Mara a single use item that cannot be reacquired/purchased by any other means? None of the bonuses of the Imperial Edition were ever advertised as being one time/single use (and many people made the decision to buy the Imperial Edition based on what was advertised). In MMOs it is extremely common for things like that to be available for every single character of the account. There was no reason for people to think otherwise with this one (plus all that was already said on 1 and 2).
I made a poll to see how players feel about it and to show it to Zenimax Online. Unfortunately, forum restrictions prevented me from posting it under any appropriate category (I went with "community events", if any moderators can move it to a more appropriate section it would be most appreciated).
Here's the link to the poll, please go and vote!
http://forums.elderscrollsonline.com/discussion/62406/should-the-pledge-of-mara-item-have-unlimited-uses-restricted-to-once-per-character