I must admit I never came across one voter at election time during telephone canvassing and door knocking who took me to task over this alleged 'fascist' current in Plaid.
The closest you can say is that elements in Plaid were close to the radical right tradition in France- Charles Maurras and
Action Francaise. Some have attempted to show that Lewis' notion of
perchentyaeth (self sufficiency) was a kind of idealised agricultural autarky a la Mussolini. These are parallels rather than direct links. Lewis did have some mad ideas- one of them being to raze all valleys industry to the ground and re-introduce agriculture in its stead, but that was never a Plaid policy- more of a personal prejudice on Lewis' part- a prejudice shared by many at the grime, ugliness and squalor of some industrial areas at that time.
The Bebb quote, often taken out of context (particualrly amongst historians with a naked Unionist new Labour agenda, including some of those mentioned above), was made in 1923 when he said that
'it's a Mussolini that Wales needs!'. this ata atime when fascism was a very new concept and the papers were writing it up in terms of 'strong man re-invigorates weak country ravaged by war'. Hence, superficially, at the very outset a figurehead like Mussolini may have had some appeal to folk trying to feel their way towards some kind of 'nationalist' polity. Incidentally this comment was made three years before the formation of Plaid Cymru- the party can hardly be blamed for that remark.
So you can see how such smears emerge- but they are easily refuted. That they are still repeated by neanderthal Kairdiff Labour typs like phildwyer reveals more about how little New labour in Wales have to say about policy or taking Wales forward these days.
incidentally, it was a Labour Chancellor of the Duchy of Lancaster who left that party to start the british fascist movement in late 1931, along with several colleagues both from labour and the ILP.
D'you think I should start a thread saying 'how fascist were Labour?'