It's hard for me to think why fstrim would have any connection to a KDE or plasma desktop problem. More likely it is something about your GPU and driver. I have been running siduction (and aptosid before that) on a OCZ Revodrive SSD for 4 years:
System: Host: imerabox Kernel: 3.18-6.towo-siduction-amd64 x86_64 (64 bit gcc: 4.9.2)
Desktop: KDE 4.14.3 (Qt 4.8.6) Distro: aptosid 2011-02 Ἡμέρα - kde-lite - (201107131633)
Machine: System: ASUS product: All Series
Mobo: ASUSTeK model: Z87-WS v: Rev 1.xx Bios: American Megatrends v: 2004 date: 06/05/2014
CPU: Quad core Intel Core i7-4770 (-HT-MCP-) cache: 8192 KB
flags: (lm nx sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx) bmips: 28021
clock speeds: max: 3900 MHz 1: 3586 MHz 2: 3400 MHz 3: 3753 MHz 4: 3400 MHz 5: 3633 MHz 6: 3401 MHz
7: 3897 MHz 8: 3709 MHz
Graphics: Card: NVIDIA GM107 [GeForce GTX 750 Ti] bus-ID: 05:00.0
Display Server: X.Org 1.16.2.901 driver: nvidia Resolution: 1920x1200@59.88hz
GLX Renderer: GeForce GTX 750 Ti/PCIe/SSE2 GLX Version: 4.4.0 NVIDIA 340.76 Direct Rendering: Yes
Network: Card-1: Intel I210 Gigabit Network Connection driver: igb v: 5.2.15-k port: d000 bus-ID: 07:00.0
IF: eth1 state: up speed: 100 Mbps duplex: full mac: e0:3f:49:e6:85:c3
Card-2: Intel I210 Gigabit Network Connection driver: igb v: 5.2.15-k port: a000 bus-ID: 0a:00.0
IF: eth2 state: down mac: e0:3f:49:e6:85:c4
Drives: HDD Total Size: 2220.5GB (34.0% used) ID-1: model: OCZ
ID-2: model: Hitachi_HTS72101 ID-3: model: OCZ
ID-4: model: WDC_WD1000DHTZ ID-5: model: WDC_WD1000DHTZ
Info: Processes: 305 Uptime: 45 min Memory: 1630.4/7917.5MB Init: systemd runlevel: 5 Gcc sys: 4.9.2
Client: Shell (bash 4.3.331) inxi: 2.2.18
I run a weekly fstrim cron job on it.
Running X as root is never recommended -- there is no solution down that path. Try booting with a "3" boot option, which should bring you to a tty login, and login there as root. Then issue
systemctl start lightdm && exit
and tell us about the error output.