I personally am a fan of talking therapy. If you are thinking something is worth asking a therapist about, it is worth asking a therapist about. But beyond the generalities, thinking you are not good enough is absolutely right in the targets of the kinds of things it can be helpful to discuss with a therapist.
Consider the propositions: 1) everyone is more competent than you at everything and 2) you can carry on a coherent conversation on lesswrong I am pretty sure that these are mutually exclusive propositions. I'm pretty sure just from reading some of your comments that you are more competent than plenty of other people at a reasonable range of intellectual pursuits.
Anything you can talk to a therapist about you can talk to your friends about. Do they think you are less competent than everybody else? They might point out to you in a discussion some fairly obvious evidence for or against this proposition that you are overlooking.
I asked my friends around. Most were unable to point out a single thing I am good at, except speaking English very well for a foreign language, and having a good willpower. One said "hmmm, maybe math?" (as it turned out, he was fast-talked by the math babble that was auraing around me for some time after having read Godel, Escher, Bach), and several pointed out that I am handsome (while a nice perk, I don't what that to be my defining proficiency).
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.