There is no drawback from doing the right thing.
The drawbacks come from when people want to do the right thing for the wrong reason. Personally I think it goes against what god wants people to do to brag about how you donate or help out a service organization and expect to get positive exposure or a tax credit.
Do it because you want to and be done with it. If you recieve a donation letter from them so be it but don't go looking for it.