I note from the cross-code forum that you are a very big RU fan. Are you against premiership RU who have P&R?.
No I don't agree with promotion and relegation in Rugby Union either.
Rugby Union struggles to support a self sustaining professional competition with the Premiership and suffers from many of the same problems that Super League suffers from. Half the clubs unable to balance their books whilst the lack of security of income leads to a lack of rational commercial investment.
The bottom line is you can't have direct promotion and relegation between a fully professional and a semi professional competition. Without a functioning fully professional pyramid like soccer promotion and relegation gives clubs false incentives, encourages irresponsible behaviour, short term thinking and is destructive.
The best analogy I can think of is County cricket where there is no promotion and relegation between the First Class and Minor Counties. The gap in terms of infrastructure, off field administration, player development structures and everything else than separates a professional club from a semi pro one is just too great. Promotion and relegation is completely unsustainable if relegation means that the playing staff have to be laid off and half the back room staff end up losing their jobs too.
The idiotic London Welsh episode from the last Union season serves an ideal case in point. A shell of a professional club with no ground, no supporters, no player development infrastructure and no prospect of being self sustaining. I would estimate that at least £5 million was wasted by the RFU, Premier Rugby and London Welsh themselves on their bid for glory. Completely irrational and there are very sound reasons why the Union Premiership had established strict minimum entry standards, unfortunately the courts of law had other ideas.