Why should FPTP still be used?

It maintains the relationship between an MP and their constituency and the geographical link between parliament and the constituency, meaning constituents are well represented.
This is done through surgeries that MPs hold to gather the views of their constituents and represent them to parliament.
Some MPs feel so strongly about their constituents’ views that they are willing to oppose the party line e.g., MP Zac Goldsmith promised he would not stand as a Conservative candidate at the next election of the party backed the Heathrow expansion, meaning he stood as an independent in a by-election in 2016.
This shows the clear lines of accountability that MPs live within because the constituents were able to remove an MP through the use of a by-election.

It stops extremist parties from being represented in parliament.
This is because an extremist minority party will struggle to win any seats unless their support is geographically concentrated.
Less extreme parties such as UKIP can still win seats for example, they won a seat in the 2015, but broad national representation is not available to them. This has been problematic in countries like France, where extremist parties have been able to be more influential, for example, Marine Le Pen, from the far-right National Rally, won 34% of the vote in the 2017 presidential election.
This shows that in without the FPTP system, extremist parties only need a small proportion of votes to begin to gain creditability.

FPTP is much easier than other electoral systems, making it less likely that voters will incorrectly complete their ballot paper.
In contrast, proportional systems often give multiple options and the chance that voters might cross too many boxes, invalidating their ballot paper, may increase.
The 2007 Scottish Parliament Elections, which uses the Additional Member System, had over 140,000 ballot papers (3.5%) that could not be counted because they were incorrectly completed.
By contrast, in the 2010 general election, using FPTP, only 0.18% of votes in Scotland were invalid.