> It doesn't really matter whether 30% of the population supports these things or 60%.

In two-party democracies, 30% and 60% are exactly the percentages that do matter.

At 30% support you can expect no change - even human rights violations will scarcely be considered a relevant political issue with such a level of support.

Once you hit 60% support, you can expect reform that won't be rolled back.

Exactly as we have seen with gay marriage in the USA. Support for gay marriage reached 40% around 2005 - I can't establish when it hit 30%, as it was rarely polled in the decade before this. Support reached 60% for the first time in 2015 - the year when the Supreme Court ruled it a constitutional right.