Anybody who hopes to debate this topic properly has to recognise that there's a lot of truth in this:
They have to deal with these facts:
Nelson Mandela was a terrorist. He went on to be the first democratically elected president of South Africa and to win the Nobel Peace Prize.
Archbishop Makarios was a terrorist. Went on to become the first president of Cyprus.
Martin McGuinness was a terrorist. Went on to become Deputy First Minister of Northern Ireland.
Menachem Begin was a terrorist. Went on to become prime minister of Israel.
Yitzhak Shamir was a terrorist. Went on to become prime minister of Israel.
This essay is worth reading:
https://www.e-ir.info/pdf/76622
As is the full article referenced in
Knave of Heart's post:
http://rageuniversity.org/PRISONESCAPE/ANTI-TERROR LAWS/One-Mans-Terrorist.pdf