In my opinion having no collide on as default for all online races that do not require you to hit someone (like infected and King) will benefit the online experience by at least 100%
As it stands now if you join an online road trip you are guaranteed to get rammed in every race by at least half the pack of people playing, this is degenerating the online experience.
Pair this with the amount of lag that you experience while playing online and you get a all out death match that ruins any fun you have while racing.
If online sprint and circuit races were default no collide would prevent the rammers from ruining other peoples fun just because they feel the need to piss other people off. Its immature and its not how racing is supposed to be done. There would be no disadvantage to having no collide as everyone would have an even playing field and racing would come down to pure skill and car choice.