What's wrong with the text?

LibreOffice Writer Xubuntu 14.04
There’s some weird text deformation when scrolling and highlighting.
What’s wrong and how to fix this? Thanks!

There has long been problems with this type of on-screen rendering. Recent GTK / Visual Components Library (VCL) changes by an LO developer has drastically improved this. It is possible that what is being seen is simply this old issue that is now being addressed.

So should I install GTK3 instead of GTK2?

You could try. Alternatively wait for v5.0.0 to see if that improves things.

How do I make Libreoffice use GTK3 instead of GTK2?

Refer this question for instructions on starting LO with different GUI toolkits.