It's IS NOT mainstream acceptance to kill so called apostates
Why 'so called' apostates, that is what they are referred to in the Koran and Hadiths.
And you are in wilful denial if you think such views are not widely accepted in much of the Muslim world.
www.pewforum.org/2013/04/30/the-worlds-muslims-religion-politics-society-beliefs-about-sharia/
"Muslims in the countries surveyed are significantly less supportive of the death penalty for converts.19 Nevertheless, in six of the 20 countries where there are adequate samples for analysis, at least half of those who favor making Islamic law the official law also support executing apostates.
Taking the life of those who abandon Islam is most widely supported in Egypt (86%) and Jordan (82%). Roughly two-thirds who want sharia to be the law of the land also back this penalty in the Palestinian territories (66%). In the other countries surveyed in the Middle East-North Africa region, fewer than half take this view.
In the South Asian countries of Afghanistan and Pakistan, strong majorities of those who favor making Islamic law the official law of the land also approve of executing apostates (79% and 76%, respectively). However, in Bangladesh far fewer (44%) share this view.
A majority of Malaysian Muslims (62%) who want to see sharia as their country’s official law also support taking the lives of those who convert to other faiths. But fewer take this position in neighboring Thailand (27%) and Indonesia (18%).
In Central Asia as well as Southern and Eastern Europe, only in Tajikistan (22%) do more than a fifth of Muslims who want sharia as the official law of the land also condone the execution of apostates. Support for killing converts to other faiths falls below one-in-ten in Albania (8%) and Kazakhstan (4%)."