Factually, that is not correct. It has been shown that genetics account for a significant factor in people who experience avoidant personality disorder as defined by the DSM under "301.82 Avoidant Personality Disorder", which is characterized by "social awkwardness" such as feelings of social inadequacy, avoidance of social contact based on fears of rejection or criticism, and hypersensitivity to a negative social evaluation from others. While your statement that there is no genetic predispositional basis may feel emotionally valid to you internally, to state there is no genetic predisposition is not factually correct given current statistical analysis. Does there also exist environmental concerns that can trigger, exacerbate, or even singularly cause such a condition? Most definitely. Does that completely negate genetic predisposition as a factor? No.
While you stated you did not want to engage in a long winded debate on it, your strongly worded dismissal does nothing to change the facts. To make your statements carry any validity to a reader burdened with anything more than a casual curiosity of the matter, your reasoning behind your assertions require much more than a reference to horse excrement to be constructed into any reasonable rebuttal of MarkRZ's reference to genetics.
As far as magicman's situation, genetic predisposition or not it is completely possible to have a great social life regardless. Genetic predisposition, while it may influence natural tendencies, does not determine the outcome. The human brain is one of the most adaptive reprogrammable systems in existence.
If magicman is facing fears of rejection or negative social evaluation (if that is), then he may end up engaging in social interactions where he is expecting to be "side-lined" before he has even attempted to relate to others. When this happens, the very fear a person dreads is often the one that they themselves cause. If you expect rejection, most people will subconsciously act in such a way to achieve that very rejection they fear. It is a simple matter of cognitive dissonance where people see themselves as being rejected even while they hold the contradictory desire to be accepted. The image of the rejection they fear wins out over the contradictory desire of acceptance. Many people lack the introspection to realize their own anxieties and to deal with them, or they recognize those anxieties but they do not think they manifest outwardly to others while they unfortunately often do.
Often key to breaking the dissonance is the realization that
(1) your worth is not determined by the social evaluations/criticisms of others or in how many "friends" accept you. If you are valuing your worth based on the number of groups of friends you "infiltrate" or how many friends are in each group, then your image of yourself is always going to be poor. There will always exist someone with N+1 groups of friends and then you will fail in comparison. Your worth is not determined by the criticisms of others or by the number of "friend groups" that accept you.
(2) That most of the people you may be afraid of being rejected by have the same deep-seated insecurity. The advantage you have is that when you are self-aware enough to know that, then you can realize a fear of negative evaluation by others isn't really an issue. The issue is your evaluation of yourself, which is resulting in your self-image of rejection. Will there still be people out there that reject you? Absolutely. Does it matter? Not really. If they reject you, it isn't something you can change or that you should even want to change (barring inappropriate behavior or not respecting other people's established boundaries).
(3) Exposure to lots of social interactions. From some of your posts, it reads like you haven't had much practice conversing with strangers. One way to reprogram a rejection habit is to get into the habit of not caring so much about some perceived "outcome" of your interactions. Learn that social interactions are not about an "evaluation" at the end of it and your interaction isn't to obtain "friendship" level with people - it is just to interact and converse. Out of that more relaxed interaction friendships will happen more naturally. Have lots of social interactions and make it a point to talk to people frequently without expecting friendship or expecting to even seem them ever again.The more social interactions you have, the easier and more natural it will be to have interactions where you aren't being hypersensitive to the prospect of rejection or dismissal.
Anyway, that is my current opinion on the subject. But what do I know? I am not a psychologist; I just come here to browse some of the cool shoes.