This is not a problem of Ubuntu MATE, mouse accelation is turned on in X. with xinput you change the settings of X for the running session. A button could be created, but it has to be developed. In the mean time you you could use one of the following options:
Turn of acceleration using xinput
or create a config file that turns the mouse acceleration off at boot:
Create the following config file: /etc/X11/xorg.conf.d/50-mouse-acceleration.conf
nano /etc/X11/xorg.conf.d/50-mouse-acceleration.conf
and add the following content:
Section "InputClass"
Identifier "My Mouse"
MatchIsPointer "yes"
Option "AccelerationProfile" "-1"
Option "AccelerationScheme" "none"
Option "AccelSpeed" "-1"
EndSection
This will disable mouse acceleration when X starts.
Just have a look on the Arch Linux wiki: https://wiki.archlinux.org/index.php/Mouse_acceleration
You could create a bash file and run it whenever you want Mouse acceleration turned off:
#!/bin/bash
#wait for the desktop to settle
sleep 5
# turn off mouse acceleration
xinput set-prop 14 273 -1
PS. Please keep the discussion civilized. We all have our preferences and we all want the best.