To start with, Any article that bases it's argument on "some experts" is obviously a biased editorial. Who are these "experts"?  Usually a group of biased leftists that agree with the attempted argument.

 But the leftist fear is that the "Independent state legislature doctrine theory" will destroy election integrity. The problem for them is that most state legislatures are made up of republican majorities and the idea that elected officials should have more power over elections than appointed judges is terrifying to them..  As long as the majority is republican.   We'd hear not a peep,  or more likely  overwhelming support, were the opposite to be the case.

BTW,  this judicial overreach was crucial to the outcome of the 2020 election.  Even if you believe all, or most of the ballots were legitimate,  quite a leap in and of itself, the rule changes up to the eve of the election were severly meta-constitutional, and this ruling, should it come down on the side  of the constitution, would make that impossible. Another reason for the leftists fear.

But what really tickles my funny bone is the argument that the words from the constitution that say the manner of federal elections shall be prescribed in each State by the Legislature thereof is just a theory.  Kinda like that "the right of the people to keep and bear arms shall not be infringed" theory I guess.   

But only if you are more committed to an agenda than the actual constitution or law.

The Supreme Court case voting rights experts say could bring 'chaos' to elections (msn.com)

The Supreme Court said Thursday it would take up a North Carolina case that centers on whether the state's Republican-led Legislature is the only entity that can set the rules for federal elections.

That argument is often referred to as the independent state legislature doctrine, a legal theory that says only state legislators have the authority to set rules for federal elections. Some conservatives have advanced that position in recent years, pointing to a provision in the U.S. Constitution that says the manner of federal elections “shall be prescribed in each State by the Legislature thereof.”