According to the Southern Baptist Convention, what is the biblical basis for involving the church in politics? I live in Kentucky, and a predominant preacher in this state is a man named Paul Chitwood, who is the executive director of the Kentucky Baptist Convention. In 2015, Chitwood wrote an article called Kentucky Baptist and marijuana. My concern is not whether a child should be taken from their parents for consuming a plant that’s less harmful than sugar. 

According to the Southern Baptist Convention, what is the Biblical basis for using the government’s aggression against people who do not live up to their own ideological standards- such as people with dependency issues?
The Southern Baptist Convention in the Public Sphere

There is no evidence that the SBC believes itself to be barred from issues relating to public policy, and there is much evidence to the contrary.  First, let's look at the SBC's understanding of the Resolutions it issues (emphasis mine):


  [...] Covering a wide range of theological, social, and practical topics,
  resolutions educate our own people about important moral, ethical, and
  public policy issues; speak to the broader culture about our beliefs;
  and provide helpful tools for our churches and entities to speak with
  authority in the public square about the biblical application of
  timely and timeless matters. [...]
  
  -Southern Baptist Convention: A Closer Look


Other Examples of the SBC opining on Public Policy

Let me give four easy examples of official SBC resolutions which relate to public policy and were given in the last three years:


Resolution on Immigration (2018)
Resolution on Defunding and Investigating Planned Parenthood (2017)
Resolution on Freedom of the Press (2016)
Resolution on Women Registering for the Draft (2016)


Concluding Answer

Paul Chitwood believes that the legalization of marijuana will have a detrimental effect on the well being of children.  He therefore decided to publicize and garner support for this issue within the churches of the SBC.  His decision to involve the SBC in a question of public policy is consistent with the stated principles of the SBC and is also consistent with SBC precedent.



(While I acknowledge that this answer is not Biblical, it does draw on official SBC sources as requested by the original questioner's bounty description, "Looking for an answer drawing from credible and/or official sources."  Given the theocratic nature of all cultures found within the Bible, seeking Biblical support on this issue may well be an anachronistic endeavor.)