You can build a left to right crawl in Motion and you might end up having to do that because Motion includes a "Reduce Flicker" option in the Scroll Text Behavior. The default action in the Scroll Text behavior is a right to left scroll, but if you use Speed Control Custom, you can offset the Start Position and End Position parameters.
The whole going into Motion and creating a Scroll/Crawl text effect is somewhat problematic. A lot of variables arise such as: length of text; length in time of the effect; and a few other inconveniences.
My recommendation would be to use a Basic Title. Type out as much text as you need for a set length of time (a good starting point would be to set the length at about 30 seconds.) Use the Video > Transform > Position > X to set the starting position of the text at the start of the title and set a keyframe. Move the Playhead to the last frame of the title and click drag on the Position X parameter until the text is completely off the screen. If "flicker" is a problem, you can adjust its speed by dragging the length of the Title in the storyline.
Once you have one Basic Title set up with keyframes (line-length and time-length), option-drag a copy of it and set it so that the beginning is appears just as the last character of the first instance enters the screen. Type in (or paste - see below) new text, adjust the length to control the speed, and so on for the duration of the crawl.
The speed of travel needs to be consistent all the way through over multiple copies of the Title. The whole crawl "system" will take some planning and once you've established a length of text vs. time across the screen. If you have a text editor that counts characters per line and is capable of providing a "Hard Wrap" at a set length of characters, I recommend using that to type out the entire crawl, then copy/paste each individual line into each Title for exactly consistent line lengths (this will be your most convenient way to set it up.) I would recommend a text editor like TextWrangler (since it's free) but it doesn't support left-to-write writing. You might be able to make do with any word processor that maintains margins (copying/pasting becomes only slightly more complicated.) If the crawl is slow enough, there shouldn't be any problems with "flicker".
Even if you used Motion to create a specific Title for a crawl, you would still be faced with the same timing/text-length issues.