I dunno, I think where Purple is coming from is totally accurate. For people who aren't really romantics, somebody else approaching them with something like that really is a great way to trigger a relationship that can blossom into love. There was a scene in Rewrite that worded it well (Rewrite spoilers) I believe Kotarou is talking to Akane about the two of them dating and is being very casual about the whole thing. Akane says something along the lines of, "But it's not like we really love each other" to which Kotarou says that they'll get to know each other better though dating, if it doesn't work out they can just break up, no big deal. Obviously, not everybody has that line of thought, and some people do want a "pure" romance, but in this day and age it's less common for dating to have such a formal air about it (especially for young people) and you really do see a lot of good relationships built out of something casual.
You're also assuming that you don't like the other party, but if they're confessing to you chances are you're at least on neutral terms with them, quite possibly even decent terms. A person confessing to you will get your mind going about the possibilities you two could have in a relationship, and if you would like to get to know that person better it's hard to beat going out. In a scenario like you're talking about where the person being confessed to actively didn't want to go out with the other person, well of course you'd just decline them and move on.
What I'm trying to say here is there's an apparent clash of your romantic ideals versus the more casual ideals presented by @Pik3rob and @Purple . Obviously you don't need to agree with what they're saying, but try to at least get where they're coming from.
Anyways I went rather off topic, but if I didn't say it somebody else probably would.