Who decides what is an "unstable and/or "immoral" regime and on what criteria?
The UK is a major supplier of weapons to Saudi Arabia. It is perhaps a relatively "stable" regime but whether it could be described as a regime that is "moral" is debatable. It is not, for instance, a "democracy" - often the criteria by which other countries are deemed worthy of support.
The UK supplied weapons to Indonesia which occupied East Timor between 1975 and 1999. Indonesia was certainly not seen by all countries as occupying the "moral high ground" - so, again, judgments as to whether a party involved in a conflict is "the good guy" are subjective and are often tied up with historical cultural allegiances but, some would argue, are mainly driven by economic considerations.
Arms manufacturers are the parasites who profit from conflicts throughout the world and who have no wish to see compromise and co-operation between and within nations. It's therefore unfortunate that our politicians - of all colours - forge such firm links with these companies. When Labour was publicly urging peace between India and Pakistan, they were quite happy to see the sale of BAE Hawk aircraft to India. Michael Portillo (a previous Secretary of State for Defence) pushed for contracts for BAE whilst in office and in subsequent years became a non-executive director of BAE Systems.