does ripple still work in practice if this default is switched to "off"?
Whether you "ripple" or not isn't an explicit setting in the client, nor should it be. Rippling happens when you extend trust to more than one issuer for the same type of currency. If you don't want to "ripple", don't extent trust twice for the same currency.
I opened an bug issue asking for an explicit warning in the client when you extend trust the second time:
https://github.com/rippleFoundation/ripple-client/issues/682Well, trusting more than one issuer for the same currency turns yourself into a gateway.
I was thinking about a path like [trusted person] <-> [trusted person] <-> [trusted person] <-> [toxic villain], where the first person seems to have a trustful network from his point of view. It doesn't matter how many people there are who you trust, even if those trust a trustful person, who trusts a trustful person, who trusts a ..., ... if it only takes one untrustful person, to compromise the complete trustline/network?