I know this has been addressed before, and received the status RESOLVED INVALID, but please reconsider.  The option of having double spaces between sentences is a desirable feature for scientific and Engineering research writing, as often we use contractions where we will use the first letter, or first two letters of a word or name, followed by a full-stop (viz. period) within sentences (such as e.g., i.e., at al., and contractions of people's names such as A. B. Citizen, and so forth), and using single spacing between sentences can make a longish paragraph seem like it consists of a single sentence.  Which can make the paragraph hard to read at times; especially when proof-reading/checking or marking.