You can use Ancestry.com without sending them your DNA. Personally, I prefer to limit who has my DNA, so I haven’t sent it out, but I know people who have and I don’t think there’s an immediate danger of doing so. I’m with you that I have a concern that DNA sent out won’t end up in various databases that could be used against me in future, and I’d rather that not happen. I know enough about my ancestors from conventional means to not think I’d really gain that much, and if I really wanted to know, I also know 30 or more blood relatives whose DNA should reveal similar information, especially if 2 or 3 have already sent theirs in. Of course, what you could do is have someone else send in your DNA sample, in which case they hopefully wouldn’t ever figure out whose DNA that really was. All that said, probably they don’t care, don’t keep that detailed a record, and nothing bad will ever happen with it. As an ancestry database/tool, their web site is pretty good and useful, though it’s also imperfect, incomplete, and depends on who else has put in data that it’s collected, which tends to be mainly English-speaking places, particularly America.