This is not the Oxford Student Union, it is the Oxford Union - a separate debating society. You can't debate things unless you know what the other side is saying. Hearing them at first hand brings out their philosophy and exposes it to disagreement and criticism.
From https://www.oxford-union.org/about_us
"At the Cutting Edge of Controversy
Unlike other student unions, the Oxford Union holds no political views. Instead, the Union is a forum for debate and the discussion of controversial issues. For example; in the 1960s, Malcolm X came to the Union and demanded black empowerment "by any means necessary". In the 1970s, Richard Nixon in his first public speech after Watergate admitted, "I screwed up - and I paid the price. In the 1980s, Gerry Adams, still under his television ban, addressed the Union's members. In Michaelmas 1996, O. J. Simpson made his only public speech in Britain after the controversial "not guilty" verdict in his criminal trial. The Oxford Union believes first and foremost in freedom of speech: nothing more, nothing less.
The Oxford Union has been at the centre of controversial debate throughout its history. As the most prominent debating platform outside Westminster it is no surprise debates have been unrivalled in their quality and impact. One of the most famous motions, "This House will under no circumstances fight for King and Country", was passed in 1933 by 275 votes to 153. The result sparked off a national outcry in the press, and Winston Churchill denounced it as "that abject, squalid, shameless avowal" and "this ever shameful motion"; some say that the result encouraged Hitler in his decision to invade Europe. In 1975, days before the referendum on EEC membership, the motion "This House would say 'Yes' to Europe" was carried by 493 votes to 92. This debate was arguably a considerable influence on the referendum result.
In the words of Michael Heseltine, the Union has "managed to absorb the greatest diversity, the wildest firebrands, the most outspoken and non-conformist people." Diversity and outspokeness, central to the Union's foundation, remain its guiding principles to this day."