People may use safety as an excuse, but the real reasons are that they are too lazy, they have too far to go, the weather sucks, they don't want to show up sweaty, etc.
If you really want to counter the safety excuse, then tell the helmet people to shut up. Nothing makes cycling seem dangerous more than promoting or requiring helmets.
After all, all you really need to do to counter people's excuse that they are too scared to ride without separate lanes is to show them the real statistics on how safe cycling really is! You don't have to go spend millions of dollars on facilities that people mistakenly believe they need to be safe: just show them that they are perfectly safe without that stuff and at statistically no more risk of injury or death than when they are walking.