For me, the problem is that the smaller a service is, the less reputation they have to lose by screwing everyone over. I don't know who you are or that you won't inject ads or affiliate links into my site in a few months (or sell your domain to someone for a few quid that will). (This doesn't mean I think your intentions are bad; I just think it's a bad idea to trust people you don't know on the internet!).

I don't mind included scripts on my page from huge orgs that have a lot to lose by doing bad things but there aren't that many companies that fall into this (Disqus did, but possible shouldn't ;))