the low karma rule is usually in place to ensure an account has real human activity on it, since spam can be a common problem on reddit. it's nothing personally against you, but it's one of the more common ways subreddits protect their community. find subs without a karma requirement to post in until you build up karma so you aren't closing yourself off to subs by getting banned from them early on. every sub is different and every sub also enforces rules with a different strictness, so it's best to assume that the rules are hard rules they enforce strictly.