There is a curious historical fact, that in ancient Rome secret ballot was introduced in 137 BC only 14 years before Gaius Gracchus, when people being able to vote for reforms but not being able to support that reforms greatly contributed to the downfall of the republic.
Moreover the main reason that we need secret ballot now, is that elections are rare, reward for intimidating someone is huge (4 years of power), and reward for voting differently is tiny and uncertain (one or the other politician not keeping promises). But with issue based voting reward for intimidating is very small as the law can be repealed when people understand that they were forced to do something harmful to themselves, and reward for not being intimidated is much more certain.
Another source of intimidation is the opinion of friends and peers, but if you support a law for which your friends do not want to talk with you, either they are not real friends or you should not support that law. In either case being open is better than lying.