That's one (rather selfish) way of thinking about it. Another way of thinking about it is that you (and everybody else) is better off if more genomic data is available for research. It's worth remembering that genomicists like George Church and Craig Venter have made their genomes publically available for all to access.
Openly sharing your genetic information makes both you AND your relatives more vulnerable, with vulnerability decreasing as relatedness decreases. It also reveals potentially sensitive information about family traits.