"Hard tyranny" is when the state makes it explicitly illegal for citizens to exercise God-given rights.
"Soft tyranny" is when those rights remain formally legal, but the state "regulates" them to an excessive degree, or selectively regulates you based upon other criteria, such that it becomes increasingly impractical to exercise those rights in practice.
As an example of that phenomena, here's a recent news story alleging "soft tyranny" against one arm of the US state - http://www.jewishpress.com/news/irs-punished-conservative-non-profits-perhaps-also-pro-israel-groups/2013/05/11/0/?print.
In the UK "gay marriage" debate, the state promises not to exercise hard tyranny. They promise not to force churches to perform gay marriage ceremonies, and that individuals' right to believe what they wish about marriage will not be violated.
This promise is disingenuous, because "soft tyranny" is already in full flow. Those who have principled disagreements with the homosexualist agenda are already increasingly marginalised. All arms of the state treat homosexuality as equivalent to hetrosexuality. In recent widely publicised cases (see www.christian.org.uk), owners of a bed and breakfast in their own home were punished for refusing to treat homosexuality as equivalent to heterosexuality; a council worker was demoted for expressing in very mild terms the opinion that homosexuals could not marry; an old man peacefully displaying a banner was assaulted by angry homosexuals and was himself arrested for breaching the peace whilst his attackers walked free. Adoption agencies that don't accept the Sodomite agenda have already been forced to close down.
Furthermore, existing law already defines a seven-fold equality agenda, and requires all arms of the state to enforce it in all their practices. Included amongst the seven is "sexual orientation". Presently, the state itself legally distinguishes between homosexual "civil partnerships" and heterosexual "marriages". However, once both of these entities are folded into a single "marriage", there will be no legal distinctions between them. It will be illegal for anyone else to make distinctions on that basis either. This will have an enormous effect, and hand a very large club to those seeking to enforce the new revisionist ideas of sexuality, to beat their foes with. This will apply to councils, schools and churches everywhere.
Moreover, it will create a massive internal inconsistency in the law. Different laws on the statute book will both forbid discrimination on the basis of sexuality (so that all "marriages" must be considered equal), but also allow the same discrimination (the government's so-called "quadruple lock" to prevent churches from being forced to carry out "gay marriages"). That discrepancy will immediately be challenged in court, and will only be resolved in one direction. (There is also the point that European courts will ultimately decide the question, and so the UK government's promises that the lock is secure are worthless - it is not within their power to keep the promise that they are making). This is widely accepted - which is why you don't hear any outrage from the homosexualists about the "quadruple lock"; they believe that it's worthless and will fall in short order so see little need to get too worked up about it.
For all these reasons, the voices telling us to chill out, and not make a fuss about "gay marriage" ("It won't affect you, since you're not gay! So why not live and let live?") are dead wrong, even within the terms of their own argument (leaving outside all other concerns). This is admitted not just by Christians, but by atheists too - see http://www.christian.org.uk/news/commentator-people-forced-to-agree-with-gay-marriage/.
When MPs are being frank about the "gay marriage" law, they admit that they believe that eventually the opponents will pipe down, go away, and forget all about it. They hope to ram the law through quickly, and then wait for the passage of time to soften the opposition, and have it all forgotten by the time another election is due.
It is the responsibility of Christians now to keep making clear to their law-makers that this will not work. Time is short, but the point can - and must - still be made. Have you emailed and written to your MP, the prime minister and his deputy, and their parties, and the House of Lords? Consistently law-makers have been receiving more letters on this issue than any other. We need to keep the pressure up.
It is also our responsibility to pray. There is a ruler in heaven, who is higher than all, and in whose hands the king's heart is (Proverbs 21:1). Moreover, it is the duty at such a time of Christian pastors to teach their flocks how to respond to this approaching triumph of the sexual revolutionaries, and to prepare Christians as we increasingly move from a society where the default assumptions are Christian to one where they are radically anti-Christian. The climate around us is changing - are the flock ready to be faithful to Christ in the new situations arising; to know when to silently weep and pray, and when and how to also publicly resist?