There is nothing wrong in wanting to learn aikido to defend yourself. It just may be hard
to sustain your commitment to the frequency of training over a length of time required to gain some modest proficiency if your only interest in aikido is defending yourself. It's a fairly common theme among many long time martial arts practitioners that they began because of an interest in being better able to defend themselves. It's also true that they found other things about the art(s) they practice that appealed to them and compelled them to stay at it over a long time.
I am in my second decade of aikido now and it's a complex relationship.
My thinking on just what self-defense is has morphed quite a bit over time and as I continue to train from week to week, sometimes the self-defense facet is large, important and sometimes I could care less because there are so many other things about my practice that I find interesting and want to explore.