Even with theoretically perfect components, so infinite Q, you can design a lowpass filter that has a flat passband, or a bumpy passband, or a round-shouldered passband, so high Q doesn't equate to ripples.
Having designed the filter shape, it can acquire or lose humps if the components you build it with don't have exactly the design values, or if the terminations it's working between don't have the design values.
Q matters. If you want to design a filter with a steep transition band, there will be a minimum Q that you need to use. The steeper the transition band, the higher the Q your components must have.
A common filter design technique is to ignore the fact that all the design tables and simple design programs assume perfect components, and then build it with components with a finite Q. The result will be a filter that is more round-shouldered at the edge of the passband than you expected. With a high enough Q, the effect will be small enough to be ignored.
If a filter has to work with such a low Q that the simple approach doesn't work, then there are tables and programs that take account of the finite Q, but this restricts the steepness of the filter response that can be designed.
Ripple in the passband isn't necessarily the worst problem that a filter can have. There is a tradeoff between the number of components, the passband flatness, and the transition band steepness. By accepting a little passband ripple, one can get a lot more steepness, a trade that's usually (but not always, it depends on the application) worth making.
