Any insurer may retain, invest in or acquire the whole or any part of the capital stock of any other insurer or insurers, or have a common management with any other insurer or insurers, unless such retention, investment, acquisition or common management is inconsistent with any other provision of this title, or unless by reason thereof the business of such insurers with the public is conducted in a manner which substantially lessens competition generally in the insurance business or tends to create a monopoly therein.