Cells have to protect themselves from damaged DNA and foreign DNA:

https://phys.org/news/2018-07-scientists-decipher-key-features-critical.html

David Comment: It is obvious that damaged or foreign DNA must be stopped at all times. Therefore this cellular defense, or some other form of it, was designed along with the appearance of DNA coding or life would not have continued from the moment it began..

Tony: Functionally, it would also prevent half-cocked additions of non-sensical DNA from foreign sources as well, preventing gradualism from occurring by methods such as horizontal gene transfer.

But horizontal transfer seems to be one of the ways evolution has progressed. I've just presented that.