Being gay is not the issue, the issue is people not marrying or having kids and dedicating their lives to it because they see other people not doing the same. Thinking that's normal is good for the individual, but not good for a society. US is doing fine in that regard, but Russia is not, population is declining, people are not marrying or having kids as much as they did before, and lifestyle propaganda is one of the few things the state can do.
http://visualbooster.com/share/20130801230340534.png Here is graph which represents fertility rate in Russia (orange) comparative to Japan (red) and Germany (blue). It's obviously climbing up since economy stabilized. Now, would you expect huge increase after anti gay-propaganda law is established?
No I wouldn't, not just because of this single law. There also needs to be actual pro-marriage, pro-kids, anti-drug, anti-promiscuity propaganda at the same time. There need to be more proactive actions and measures taken, but of course that's much harder than some blocking measure.