Increasingly, there is talk that permitting Huawei to bid on telecom network contracts makes a country vulnerable to espionage and worse. The Economist has a well argued ripost. Well worth a read.
The other reason for not banning Huawei is the dirty little secret that its foreign rivals strangely neglect to mention: just about everybody makes telecoms equipment in China these days. Chinese manufacturers and designers have become an integral part of the global telecoms supply chain. Blocking Huawei (or its rival Chinese telecoms giant, ZTE) while allowing gear from, say, Alcatel-Lucent or Ericsson on a network may make politicians feel good. But it is no guarantee of security. Huawei’s competitors have a vested interest in hyping concerns about it, while disguising their own reliance on Chinese subcontractors and on subsidies.