good means, good ends - no need for justification
bad means, good ends - the ends justify the means
good means, bad ends - the means justify the ends
bad means, bad ends - no possibility of justification
UK terrorism is bad means. UK political change is good ends. If the ends didn't justify the means, they wouldn't be good ends. Any statement that the means were bad but the ends were good is justification; otherwise, your opinion would be that because the means were bad, the ends were necessarily bad too, even though they would otherwise appear to be good.The disconnect is that I don't accept this assumption. I see no evidence that the US method fights terrorism better. In fact, it appears to result in far more and worse attacks than the British method.
Therefore, I am advocating for something that I believe will mitigate terrorism as it happens, and produce a better outcome. Thus falling squarely in the "no need for justification" line of your summary.
They stopped their attacks when their demands were met.
I fail to see what you are advocating other than giving in to terrorism.