Far from deterring an attempt by China to achieve reunification with Taiwan by force, might sending weapons to Taiwan actually encourage a military scenario?
Preparing for a military conflict in Taiwan, like in Ukraine, may only make one inevitable. The arming of a hostile power on the doorstep of one's "enemy" can only be perceived by them as creating a springboard for damaging them via some form of provocation and border conflict.
While war is not preferable, having an enemy constantly knocking on your door and making menacing sounds about its military power at your doorstep requires countermeasures. Taiwan's development of missiles that can hit mainland China ought to be of particular concern to Beijing's military experts.
From Ukraine to Taiwan
If Taiwan is at the command of Washington, as Beijing no doubt suspects, then the US could encourage the outbreak of a local conflict at any time of its choosing in order to damage China. As we saw with Ukraine, it seemed that everything was done to provoke the Russians into what the US hopes to be a costly occupation and a strategic defeat for them.
Ever-increasing stockpiles of Western weapons, bellicose rhetoric and eventually a threat to build a nuclear weapon were undertaken by Ukraine's government prior to Russia's attack, almost as if they wanted to do whatever it took to convince Russia that an attack was the right move. Clearly, China also has red lines with Taiwan. If Taiwan announced that it would build nuclear weapons to "deter" China, for example, this could prompt China to take military action urgently in Taiwan.
Western talking heads and politicians will have us believe that arming Ukraine gave the Russians pause and made them think twice about what they were already planning to do. There is no recognition of the fact that an opposing alliance pouring its weapons onto one's doorstep might actually provoke the military action one hoped to deter.
Put yourself in their shoes
If you ask someone here in the UK, there may be an almost a complete inability to see this situation as the equivalent of Russia arming an independent Texas against the US or China arming an independent Scotland against England. Many minds won't be able to process that comparison, because of a failure to even momentarily identify with the "enemy". The badness of the enemy is taken to be an uncontested fact that even the "enemy" population must surely see.
I see an inability to comprehend the idea that the other side might think similarly to us, almost like a failure of the theory of mind (the ability that arises in infants to understand the motives of others, by realising that they also have mental states too). Without a theory of mind, you will be unable to tell if someone else will resist being stabbed with sharp sticks, like you would, because you are no longer able to imagine being in their position. You might imagine another person as some unpredictable monster and attribute everything to this, rather than trying to understand that they are an agent like you.
Of course Britain would take military action against another country that tried to threaten us by arming an enemy on our doorstep. Even if many soldiers died, the patriots would insist on sending more, and heap praise on the fallen. No foreign weapon supply would deter us in that situation, and in fact it would just outrage us and encourage us even more. Unfortunately, we are now unable to imagine that other countries might think similarly, even when any glimpse at the facts will show that they do.