Don't feel bad about preregistering a .xxx gTLD domain name.
When the program was announced, the adult industry did not have a clear understanding of the goals and ramifications of the .XXX gTLD program and had not organized itself in opposition. Moreover, several major adult players came out in support of .xxx at that time. Many people registered domains during that time as nothing was seen as being wrong with the registrations. Since that time, many have registered their .com domain names in order to protect their existing businesses.
Neither situation should be a cause for embarrassment as the actions occurred either before the ramifications were clear or in order to protect your existing domains which are both reasonable business decisions given the situations.
As ICM has said that preregistrations will not be used as a sign of industry support, potentially, no serious harm was done.
Now, knowing what we know, just be sure to show your opposition to .XXX when asked by your trade association, the Free Speech Coalition.
Just my personal opinion.