It's true this pattern of "Accept <wrong> to prevent <worse>" has nothing to do with left or right. However I don't think it applies to pro-gay propaganda, because the whole point of the left-wing stance on this issue is that there is nothing wrong with being gay in the first place.
Side note: the pattern "accept <wrong> to prevent <worse>" is of course not bad in itself, but rather when false assumptions are used to connect <wrong> and <worse>...
I stand corrected - being a liberal (in the original sense, not a leftist) I used to consider all propaganda as bad. But there's indeed a 'good' propaganda. Or at least 'not bad'.
Side note: the pattern "accept <wrong> to prevent <worse>" is of course not bad in itself, but rather when false assumptions are used to connect <wrong> and <worse>...