I'm sure that a sizable portion of those who are strength training are doing so because of an insecurity of some kind. I know that it was certainly a catalyst for me to start getting stronger. I wasn't heavily bullied as a kid but I did receive a share of it since I was on the bad side of being skinny. Still, I don't think it was a bad thing per-ce. It was part of a conscious decision to get myself stronger and more fit. At the end of the day, I'm no doubt better for it.
Insecurities don't need to be bad things. If we look at it, they are telling us something about ourselves. If we're insecure because we're too weak, too thin, too fat, etc then we are getting a message from ourselves (and outside sources too) that something isn't right. Now, it wasn't right that I got bullied because I was small in school but it did teach me a lesson about life in general: BEING WEAK SUCKS! Weakness isn't a quality to be maintained. It's something that needs to be corrected. This insecurity motivated me to correct this in myself. Now, I'm definitely a better person for it.
Don't allow yourself to be crippled by your insecurities. Use them as a motivating factor. Accept the fact that this could be your mind's way of telling you that there is a situation that needs to be corrected. Then, set your sites on fixing this. Insecurities will only make you a worse person if you allow them to exist to do so.