I won’t argue that the editor should not crash on imports as that can be rather frustrating. I’ve not had any experience with Unity or CryEngine with how they import or any errors they may throw (assuming you were referring to one of those available engines 
).
A lot of the crashes I have seen users report since the release of 4.5 have been related to the new method of auto-generated Lightmaps UVs during the import process. There were two reported issues related to auto-generated Lightmap UVs that would cause a crash. The way to avoid this was to uncheck the option to generate them on import (at the very top area) so that they are not generated and causing the crash.
This bug is high on the queue, but a fix has not been checked in as of yet.
If you’re able to import after unchecking this import option then this is a known issue. If the crash is still occurring with this unchecked there is something that can be looked into and see if I can get repro on my end.
I’m certainly not trying to dismiss any crashes as “fix the source material” especially if a repro can be found. It’s much easier for a developer to fix an issue if there is a solid repro that can happen with things other than a single mesh. If it’s just a single mesh it may be something that is corrupted or wrong with that particular mesh. Being able to use the same steps and recreate the crash with any variation of mesh makes it much easier to look and see where the root of the problem may be coming from.
That being said, if you have a set of repro steps for creating a mesh and getting the crash I’d be happy to look at that and see if I can help. 
I know you mentioned getting meshes from online resources. This is fine, but often times these will need to be adjusted to be “game-ready.”
Let me know and I’ll look into this further.
Thank you!
Tim