I knew is was intentional but it's kinda weird to neutered an ultra-expensive item to uselessness. Not to mention that you can't see the laser when using point firing which defeat the purpose of it.
You asked why you can't use it that way as a support question, but you also knew it was intentional? Please leave feedback in the comments as this is for issue/bug support. The appropriate way would be to simply ask "hey can we get a config option to allow the use of sights with thermals?" like Andrew did.
I will add an option for it whenever there's a new version of Realism.