But at speeches given at universities since his return, students have crowded out assembly halls. On home ground, the 69-year-old former National Taiwan University professor, for whom an arrest warrant was still out until last year, is being lauded as an intellectual mentor for the opposition movement. He has also become something of an ethical steward for the high-spending parliamentary elections being held today, in which 406 candidates are contesting 161 seats.
The elections offer an imperfect watershed in Taiwan's transition from the authoritarian strong- man politics of the Chiang Kai- shek era to a more democratic system. The ruling Kuomintang (KMT) party will win comfortably, because the main opposition party, the Democratic Progressive Party (DPP) is fielding only a limited number of candidates. But it will be the first time for more than four decades that all the seats are up for election, and the first time ever that the entire parliament is being chosen within Taiwan.
The last full election for the parliament - the Legislative Yuan - was in 1948, when Chiang Kai-shek and the nationalist KMT were still on the mainland; but it was only a year ago that the aged survivors of that election were finally forced to retire. Today's vote, albeit blighted by vote- buying and the biases of a former one-party system, will be a decisive step in changing the Legislative Yuan from a rubber-stamping body populated by snoozing geriatrics to a functioning parliament with a meaningful opposition. According to David Shambaugh, editor of the China Quarterly: 'The simple phenomenon that the elections are taking place is very important.'
Taiwan's democratisation has been a comparatively brisk and bloodless transformation. It was back in 1964, 15 years after the KMT had lost to the Communists and retreated to Taiwan, that Mr Peng was arrested and imprisoned for preparing a manifesto calling on President Chiang to admit the absurdity of a 'One China' policy and to concentrate instead on building up Taiwan. Six years later, after prison and house arrest, Mr Peng escaped via Sweden to the United States. But it was not until July 1987 that Chiang's son, President Chiang Ching-kuo, decided to lift martial law. And it was only in May this year that President Lee Teng-hui, the first Taiwan-born president, who took over in 1988, abolished the sedition law which made it illegal even to discuss Taiwan independence.
This month's election campaign has been dominated by two issues: the increasingly complicated argument about Taiwan's future relationship with the mainland, and electoral corruption. In rural areas free banquets, concerts and even a chess tournament have been on offer - as well as hard cash.
Mr Peng, who is backing the DPP as the only viable opposition party, says: 'I am disappointed. The corruption is an open secret. This type of corruption will destroy the democratic process of the elections.' The state-run television stations and pro-KMT newspapers are also accused of ignoring or misrepresenting the opposition.
Rival policies towards the mainland are the central political issue. Taiwan's de facto independence and its growing business ties with China are becoming more relevant than old-style KMT claims to sovereignty over the whole of the mainland. In five years there have been more than 4 million visitors from Taiwan to China; and Taiwanese investment in China, usually via Hong Kong companies, is estimated at anything up to pounds 2.55bn.
The DPP is running with a 'One China, one Taiwan' banner, a softer version of its strident (and technically illegal) independence platform in the National Assembly elections a year ago, which appeared to put off voters. Mr Peng says: 'The big issue is whether we should concentrate on building up a democratic Taiwan.'
The KMT is split between a progressive wing of mostly Taiwan-born politicians who privately seem little removed from the DPP on the independence issue and the old-guard mainlanders who stick to the One China ethic, which for the time being is really about prolonging the status quo. Professor Chu Yun-han, at the National Taiwan University, says: 'This is a very emotional issue. The (former) mainlanders support the principle of One China but recognise that it is foolish to talk of reunification at this point. The Taiwanese KMT do not support it but also recognise that now is not the time to jeopardise the relationship with China.'
In Peking, Jiang Zemin, the Communist Party's General Secretary, said China would not hesitate to use force if Taiwan declared independence. 'We've heard it all before,' says the DPP. 'It is an insult,' says Mr Peng.